Are you saying that you've had Oracle failover successfully, between 32- and 64- bit machines? I could see that working if the version of Oracle was 32 bit mode only, but if Oracle is 64-bit, then I would expect to see problems if it failed over to as 32- machine. At least performance issues. I wonder about how the SGA would function if it was initiately configured in 64- and after failover, was running as 32? However, I'm not an Oracle expert ....
HTH