Dragon Tail + Earthquake Steelix should be listed as a tank counter against the Jolteon raid boss
I know it doesn't have the DPS, but it has a really high base defense stat and the steel/ground typing, which reduces approximately 49% damage. I think, it might be useful in group raids with 2 people.
Answers
I raid with the wife regularly and since 2 people can easily win against Jolteon, there is little need to tank damage like an Articuno or Lugia raid to get more premier balls...I think EVERY Level 3 raid, we always get at least 11 balls (5 + 3 damage + 3 team bonus) And sometimes 13 balls if we have the gym.
On a raid that you can possibly lose your team and the damage bonuses, then I can definitely suggest tankier mons to not have to swap out (and get more premier balls for those hard to get legendaries).
I hatched a 100% Onix yesterday, evolved it to an Iron Tail / Crunch Steelix, and I just can't quite justify investing the TM's and stardust because I don't know what it would be good for.
I'm not sure why I would even take on a Jolteon raid since I'm swimming in Eeveelutions... so this isn't really a good motivation.