Michael -- thanks for the tips about the WMI calls. You were correct -- "The RPC server is unavailable" "0x800706ba".
I did some internet searching and most of those similar issues talked about firewalls, etc. I re-tested that route (Group Policy forces the firewall off) and even restarted the WMI services. Then while testing it dawned on me -- we recently had some issues with another product IPSwitch What's Up Gold. I know WUG uses WMI calls too. The resolution for those WUG issues was reverse lookup zone (PTR) records being incorrect in DNS.
Sure enough...I found/fixed the PTR records for those servers I could not add to Balance and wala...
Balance can now properly add these various physical servers via IP and FQDN.
I'm assuming the Balance product uses some sort of reverse lookup or WMI call when attempting to add a new device to monitoring.
So for anyone out there with issues like this -- check your DNS infrastructure and then re-try adding servers to Balance.