There may be several different board and ASIC versions used for the PERC6, some of which might be compatible and some might not. The PERC4 and PERC5 family had about a hundred board and ASIC versions. OK, not that many, but enough to make answering this question a major pain in the arse with lots of boards killed during experimentation. e.g.
"Yeah, I think that one is compatible."
"OK, I force flashed the LSI BIOS and the board doesn't work."
"Ehh, which week and board revision did you say that was?"
"23rd week, Rev. 1.06, Malaysia."
"Oh, right. That one used a newer ASIC from LSI and was not compatible. If it had been 21st week R1.06 from Malaysia, it would be compatible. I was thinking of the 23rd week R1.0x board from Costa Rica. Sorry about that."
"GAAAH!"
(I made-up those particular details, but you get the idea.)