In doing some research, it appears we've narrowed it down to the fact that the proxydhcp service is responding by sending broadcast packets, rather than unicast. Is this normal? (Log info from our switch, showing that packet was denied)
list al_104 denied udp XXX.XX.104.37(67) (FastEthernet0/42 0014.2233.3bbc) -> 255.255.255.255(68), 1 packet
The oft cited fix to getting this PXE to work with various VLANs is to configure IP helpers, but the question is, doesn't that just fix client traffic, and not affect the fact that the proxydhcp service is blasting out responses via broadcast?