Hey,
I actually have somewhat fresh memories from having played on a similar project server around 5 years ago and ranking top5 in all seasons, at over 2.9k rating, as Rogue/Mage. What I will be discussing about below are S5 and S6 metas:
In terms of damage, feral is very strong. Warriors, not so much, due to limited damage output in a meta with many hpals and disc priests, rage generation being the main issue. Hunters will be lacking due to the pets dying very easily, with the low amount of HP and resilience. Destruction warlocks can be strong, but are again, countered by killing their pet easily.
The best option will actually be DK, since casters and healers lack mp5, and DKs are still kings of overall-damage and defensive cooldowns (coupled with the paladin's), shining in the short(er) duration arenas.
As a conclusion, Feral will be strong, but it doesn't have the best synergy with Hpal due to the limited offensive toolkit a Paladin has. One suggestion would be to try the comp as a 1H Ret/Prot build, to offset that. (You get more damage, repentance as an additional CC, while maintaining strong defensive capabilities & healing).