This is realistically only fair if they disallow gearswapping anything but trinkets and weapons in the arena as it penalizes warlock/shadow priest 2v2 and 3v3 teams far too much. Remove the ability to swap into resist gear and then whatever changes that can be made to dots to apply resilience effects to them are completely fair. Effecting dots by resilience and allow people to stack SR as well and you destroy that teamup.
All other casters are affected by resilience and resistance to though, and SR is actually a really hard stat to boost with a decent kit pre-BT.
It's the same answer on the public forums and here, and I frankly think people are overestimating the resistance gear. Provided the dot gets through, you will still get full 75% 50% 75% etc damage, but your other stats will be very gimped, leaving you at disadvantage again. Also, a gear set with proper resilience and resistance would leave you defenseless and without any offensive stats whatsoever.
Just to update this thread, Blizzard has listed this issue in the "known issues" thread AND said that it will be fixed! Blue said that it's been listed as a known issue for a while, but I hadn't heard that from anyone else. Anyway, here's the snip:
Spells, Talents, & Abilities
* Critical strike damage reduction percentage gained from resilience rating increases as the attacking player gains more +critical strike damage bonus talents.