Yes, and that actually might be a good idea. You can use one to cross-check another; if a virus is caught on one--but not the other, you would know that one virus checker was weak or not up-to-date. It would be slightly more maintenance (keeping 'em straight), but the network would be more secure as a result.

If the PCs on the network are similarly provisioned, it would also allow comparisons as to effectiveness and resource usage between programs.