Depends on how your routing works. Generally speaking, no, not without source NAT to one side or the other (which is bad for anti-spam appliances), and not in a way that's geographically redundant, where using a single public IP. Multiple MXes with separate IPs is the best if not only option for redundancy. There are options, tends to get complex though. Probably more than you'll find reasonable help with on a forum because of the complexity. Would be a good fit for professional services.