Uhhhh...can you read? Because that is really all you have to be able to do to check WSUS Offline since the GUI is really just a front end for some scripts which are in a folder appropriately labeled "cmd" so you can just open them in the text editor of your choice and see what its doing.
It also doesn't try to obfuscate in ANY way what it is doing or who it is calling if you are using the Offline Generator to generate an Offline Update client (it currently supports Vista-10 including the server variants, VERY handy to have) so when you launch it you get a standard command prompt where you can simply look at the screen and see its just calling the MSFT update servers and downloading the updates straight from the source.
Let me give you my personal assurance, I've been using WSUS Offline for so long I still have the DVD with the WSUS Offline for Windows 2K Pro and not once has there ever been an issue with any kind of spyware, malware, or even Windows Update issues because this doesn't use the WU client and just installs them manually via script. I can't even count how many clients I've used it on, easily in the thousands, and its one of those tools I'll always keep on my network share, its head and shoulders better than dealing with WU.