There was short time after Forge was being upgraded to 1.8 where RenderPlayerEvent was NOT fired (because it was WIP).
I am not sure if your version is in scope of said time, but:
1. You can find out in changelog - look for log saying that RenderPlayerEvent was reactivated.
2. You should update to 1.9+.
Aside from that - why the hell are you registering same event class for 2 buses? Separate your FML and Forge events in 2 classes - otherwise it's waste of resources (okay, well - micro optimization).
Next on plate: As of 1.9 (I think, maybe earlier) FML and Forge buses were merged into one - so basically no matter what you call - its same event bus - thus call it only once. Said that - update to 1.9+ and use one bus for all events (not mentioning decorator ones).