Unfortunately, the only real response to "Do Macs support ASM" is "which one?" Every processor has its own form of assembly language, and it is usually very hard to port ASM code written for one processor to another. This is one of the reasons high-level languages are so commonly used today: it is much easier to port such code between architectures.
So the real question here is this: what computers does this program your friend wrote run on? Without that information, it's not really possible to answer the question. My guess is that your friend probably wrote it in Intel ASM, in which case it should work, but only on Intel Macs. In order to support PowerPC-based Macs, he would need to rewrite it in Intel ASM parts in PowerPC ASM. I highly recommend that your friend do this; porting from Intel to PPC is much easier than the other way around.