I called VMware to see if they have a fix. If you connect direct to vCenter, the MOB shows the VMware Rollup Health State to be "unknown". However, if you connect directly to the host (not going through vCenter, you can see the proper status of this. I have two ESXi hosts that display properly in VEEAM and two that show "unknown". I can correlate these values exactly when I look at the MOB through vCenter. So I'm fairly certain that VEEAM is getting this specific value from the MOB.
VMware didn't have a fix or workaround, but said they have been working with VEEAM on this and expect a fix in Update 2 for vCenter 5.1, whenever that comes out. For me, this issue started after I put on the VMware patches from October.