I've not used DS 5.2 on SuSE.
But, one other note for your boss, regarding the specific supported RedHat version:
DS5.2 p4 is officially supported only on RHEL3, which uses the Linux 2.4 kernel. SuSE 9 uses the Linux 2.6 kernel.
So in addition to using an unsupported Linux distribution, you'd also be using an unsupported Linux kernel.
My hunch is it may be difficult to get support from Sun if you run into problems with this arrangement. However, if you don't need Sun support, maybe this doesn't matter so much.