Everyone agrees that you cannot administer an NT machine with Linux "out of the box", yes? You have to add some glue code. That glue code is going to receive requests over the network, whether it is BigBrother, Monitor, SNMP, or god forbid a webserver. I don't see why an existing NT server or workstation cannot be used for this. Although you can justify buying more licenses, there is no reason for it.
The webserver option I proposed may not be acceptable in this environment, but it meets the requirement given: the ability to execute system calls against/on NT from Linux.