Is thunderbolt pairing Jolteon (80% IV, 14/12/10, ATK/DEF/STA) good to put in gyms?

Yes! Faster charge move can help in battles!

Jolteon is terrible on defense, soooo weak. On attack he is great though, if you like to dodge thunderbolt Jolteon is awesome.

There is no right answer but Jolteon has low HP so cant take many hits, hes a lightweight dancing in a crowd of heavyweights.
Whatever you do, do not power up jolteon. Ampharos is coming.... Hes gotta be one of the most anticipated of gen 2.

I would never put Jolteon in a gym - with such low stamina he'll get eaten alive. I think Jolteon's best use is as an attacker, where you can mitigate his low HP by dodging.