I don't know jack squat about Lake Roosevelt, but you might want to try Anton Jones at Darrell and Dads Guide Service in Chelan. He's a full time lake guide in Central Washington and will probably have some info for you. Here's his website:
I'll check those guys out. Going to head over this fall...not much info out there for those upper Columbia reservoirs...local bait and tackle shops and guides probably my best bet for info.