I don't think so, even though its the same card technically, I really doubt the drivers would work with both cards, its like saying the 8800 GTS will SLI with the 9800 GTX.... I doubt it will work. Unless you flash the 9800 GT into a 8800 GT, but thats just not worth it.
Apperently what I read was that there are 2 9800 GTs, 1 55 nm and the other 65 nm.
I think it would say on the box, or if you already have it in your computer download a program called GPu z
ivbeen told that you can mix 8800gt with 9800gt but they will only run as fast as the slowest card. but since they are practicly the same card anyway. its a good point about driver surport tho! i serpose you must have to use both 9 & 8 series drivers. it should work! afterall your sound card drivers dond get mixed up with you're ethernet card drivers for example. so why not.