When you installed the PowerChute software, did you install it on ALL servers? If not, that's what you need to do. Also, make sure you configure the software correctly. For servers on BASIC signaling ports (#s 2 thru 8), you need to select BACK-UPS with SIMPLE signaling even though you may be using a SMART-UPS. On the advanced port (port 1), you would select SMART signaling and the actual UPS type (SMART-UPS, BACK-UPS, etc).
When you said you can communicate with the servers via IP or NETBIOS, were you talking about via the PowerChute software or network neighborhood?