I had my DVDRom (Pioneer 10x) as Slave in UDMA mode and CDRW (Yamaha 8x8) as master for quite a while and it worked fine.
I always did create image on hard drive, then burn image to CDRW at 8x.
Works fine, takes less than 15minutes.
Going DVD to CDRW direct might cause some troubles though. Not incompatibilties, but just bus contention. IDE isn't very effecient with multitasking, and esepcially with the DVD Rom being in UDMA mode 2 and the CDRW in PIO mode 4 it's extremely difficult for IDE to keep up a decent transfer rate between the two...(And if you put your DVD in PIOmode4 DVD playback takes a nosedive) you might get buffer underruns.
Of course if you have a plextor burnproof this isn't an issue
