Is this Snorlax useless?

No snorlax is useless

moveset ratings are relative to the pokemon's other movesets. a snorlax with a weak moveset and 0% IVs is still better than most pokemon in the game just because of snorlax's high base stats. i'd rather have that than a 100% IV "perfect" moveset onix for example.

if you've got a pokemon with a weak moveset and/or unacceptable IVs (for your standards) just don't power it up further, in the future you might hatch a snorlax from an egg or find one in the wild with better moves and/or a higher level, which would be worth using candies on.

but you can still use it as it is right now if it's got high enough cp. also whats your trainer level as well as the snorlax's stats.

for example I caught dragonite with 15A 14D 1S at lv 11 with DB/HB. it's now lv 14 (powered it up 6 times). I can still use it to combat gyms in it's current state but I'm not going to power it up further because I have a few dratini with better IVs that could also potentially get better movesets when I get to evolving them, but I can't fight a gym with a dratini, so there's no reason for me to get rid of the dragonite.

also with trading being a potential future update there's probably going to be plenty of people out there who don't care about IVs or movesets as much as they care about having a cool/rare pokemon.

I don't see the point in transferring such a rare pokemon just to power up your other one one more time, the difference that one extra power up gives is marginal.

Still a decent defender (and attacker as well). Nothing (arguably) except Lapras/Dragonite/Snorlax would be better for general use at the same level (not CP).
If it has decent level it's quite fine for defense...
If not, throw him in anyway. Unless you have others with similar/better CP and decent moveset.

I personally wouldn't power him up for now. As you have no other good defender, your level seems to be still rather low (<25, right?).
If true wait with power ups (unless you have excellent moveset+IV). Usefull defenders (or bad defenders) with good level will fly in. Hypno of low IV and your level should be found fast and is a good defender (low CP thus kicked out fast). Gyarados can be walked to high level quickly, is a bad defender, but who cares if you are #3 of a lvl10 gym. The others do the real (defending) work.

Even a rusty sword is still a great club.

Snorlax has one of the highest hp in the game, and if you use it as a defender in a gym, that hp is doubled. With a high enough CP, you'll be able to put the Snorlax in the upper levels of a high level gym, ensuring that even if the gym is attacked, your Snorlax won't be the first to be kicked out. (FYI, your 60 % IV Snorlax will probably break the 2000CP mark at pokemon level 24.)

You wanna use that Snorlax for something? Put it as your Buddy. With the current Halloween event, you'll get back the candies you've spent on powering up if you walk a lot. The limit for walking with your buddy each day is 40km, meaning you can get a maximum of 32 Snorlax candies daily during this event. At the time of writing, there's supposedly at least 24 hours before the end of the event.

All these candies can then be potentially used for powering up your next good iv + good moveset Snorlax. No matter what pokemon level that Snorlax you catch is, you'll be able to power it up as much as possible and use that Snorlax in your gym immediately.

Additional info/details that you might already know, for your consideration:

FYI, it takes 66 candies to power up a pokemon from level 20 to 30, so if you hatch a level 20 pokemon and you are at least level 28 with enough candies and stardust, you'll be able to power that pokemon to level 30 immediately. At level 30, it will be at 90% of the maximum CP it will have at level 40.

During a battle, most players go with one of two different tactics when it comes to dodging. 1) Dodging every attacks, or 2) dodging as little as possible. Thus, when facing a Snorlax, the attacker will typically either bring out their strongest pokemon to take him down as quickly as possible while only dodging charged moves, or bring out their 2nd/3rd strongest pokemon and dodge all moves, preserving their strongest pokemon for whatever comes next.

However, with the high amount of hp a Snorlax has, if you dodge every moves, you'll run the risk of not being able to beat the Snorlax before time runs out. Not to mention, your particular Snorlax has Earthquake, which is hard to dodge for some people. And quite honestly, if a player is using the dodge-every-move tactic, he/she will probably be skilled enough at dodging that a Snorlax with Hyper Beam will never hit him/her, due to the long startup animation of the move.

As an aside, you do not want to put a low CP Snorlax or Lapras in the gym, even with the recent changes to the gym mechanics, which allows a player to bring 6 pokemons to train a gym. A Snorlax has no real viable counter in the current metagame, and if anyone use low CP pokemons to try and earn the highest prestige possible, they will be unable to do so with ease with your Snorlax defending the gym at the lowest level.