You should probably give Azonic a call. Im pretty sure that there isnt enough room on the Recoils to run a shock with a standard piggyback. If I remember correctly the Recoil only came with the Romic for that particular reason.
it should be fine to run a 5th element. A friend of mine had a swinger 6 way on his with no fittment problems. He had his mounted so the piggyback was set at the bottom and facing the bb. Seemed to work no problem.
8.75x2.75 5th Element works fine. This is the shock that the Xtension bikes (same as the recoil) came stock with.
Also, the frame should work with 9.0 x 2.75 and 9.0 x 3.0 shocks if the piggy back fits within the frame. Since a a smaller 5th works without any issues the others you have listed I would think would work, however it is always best to check.