I'm running a team of Ackbar (L), Luke, Biggs, HR Scout and RG on the arena on my little account (@ lvl 54 currently, in a relatively new leaderboard - meaning that the top of the board is around 57-58). Admittedly, Han would probably be better than RG, but I do not have access to him yet. Ackbar 5*, Biggs and Scout 4*, Luke 6* and RG 2*.
My experiences are extremely positive so far. At least on this level, the team beats practically anything that comes up in the ladder and mindless (the only comps I have to think against are the ones with RG's auto taunt). The speed is the essence, with Ackbar in the lead, very few characters get a turn before Scout, Luke, Biggs (and sometimes Ackbar himself though he is slower). Now, these 3 can kill practically anything in one turn, in most cases without Biggs' special, so you are most likely to eliminate the biggest threat on the enemy team before they even get a turn and from on, with RG's taunt, they can just kill everything else with their basics, which are also doing decent damage. In addition to that, Ackbar's first special is the perfect Sidious counter - consuming his debuffs you can practically heal up your entire team to 100% health at the begining of your 2nd turn. And there are _a lot_ of Sidious' around.
Bad side is, they are extremly weak on the defense - most days I go up to top 50 (with higher level ppl around me), but due to being unable to play around the reset, I usually end up in the top 200, or lower.
All in all, even though my experiences I far from endgame, I found the Rebel team extremely fun to play and at this state, they seem to be more than viable for me. (Only if I had some great defense chars, they would even be better...)
