Yeah, I never had FCP 3 on my Pismo, but a Pismo should run FCP 3 on both OS 9 and OS X. As per usual, OS 9 will be faster for that task, but OS X may do it slightly more reliably.
I never had trouble doing basic DV capture, cutting, titling, and a few basic effects on my G3@450. I had anywhere between 384 and 896 megs of RAM, a 20-gig boot disk and a 120-gig capture/scratch disk, so it was not crazy but it was set up well for what I was doing.