You're too kind !shy
I can't imagine how they've managed to get it working, but it really shouldn't be this hard !! I had a bit of a deeper think over a large brandy and it occured that there are a couple things to try but whether or not anything will come of it who knows. First, it might be worth running "sc query" from a command prompt on your windows server to see if there is anything spurios or obviously different about the service name. Sadly, "sc" doesn't have much to offer in the way of other information, but luckily there is a handy tool available from microsoft (now anyway, used to be sysinternals) called "psservice" which is part of the pstools suite of 'groovy stuff'. If you can grab that (less than a meg) and unzip it, give "psservice security " a shot. That'll show you a useful view of which accounts can do things like query the status of the service - you'd want to hope that the account you have nsclient++ running under (local system?) would have that privelege!
As I say, whether or not either of those will reveal anything useful is anyones guess, but, one hopes that at least either one or both of "psservice query " or "sc query " will be able to see and reveal "STATE : 4 RUNNING" for your service, and if so, this is ultimately good news. That means if push comes to shove you can at least slap something like Perl on your windows server and write a little script to run that command and capture the STATE from the output. Then use something like NRPE to call the script from your nagios server to check the status of the service - job done! OK, it's a cludge, but if it works and saves you money in the long run, happy days Who knows... have a look-see if NRPE is already installed... perhaps that's how they are doing it!
Any road up, time for another large brandy. Keep us posted on your progress!
PS Get psservice here