There's lots of circumstantial evidence, I think.
First: Russell came to Parv, and stated he wanted an alliance. Parv stated that "she felt he was doing that with all the others." I don't think he was though.

But that was his game in Samoa, first time. How would she know that?
Second: She has never considered cutting him loose. Why not? Maybe knowing he was a sure bet from day one to beat in the end?
Third: Her friendship with the casting director, Shay, who also casted Russell.
Fourth: the alleged recent firing of the same casting director, Shay. Coincidental too?
Fifth: Sugar has backed it up somewhat... and what she said was BEFORE all the other stuff came out. It's not like she's jumping on a wagon here.
Sixth: this burning incident. It's way unbelievable as just "coincidental" with all the other circumstantial evidence mounting.
This irritates me to no end. I'm going to be looking for as much info on this whole thing as I can!