No, unfortunately OpenSNES9xGp saves cannot be read in SNES9x or ZSNES. The save state format is actually closer to ZSNES, and OpenSNES9xGp CAN read ZSNES save states...just not the other way around. I believe this has to do with the image information stored at the beginning.
However, remember that SRAM data is universal.
And yes, the saves ARE compressed, but I think it's the image data which is messing them up.