I have 15 VM's running for clients and I'm looking for a way to keep the tools up to date without having to connect to each server and do it manually. A few examples are WinDirStat, Firefox, SSMS, Filelocator, etc.
We have expanded recently and I'm at the limits of doing this manually. These servers are not domain joined and are in separate virtual networks.
Yeah for sure. From a security perspective s domain acts as a boundary though and when done correctly adds protection. 15 VMs all windows based would benefit from this and would add very little overhead.
Creating an AD domain carries a substantial amount of extra overhead that they might not want to deal with. The basics of setting one up are simple enough but actually building out/maintaining the infrastructure the correct way can be a lot of extra work (2 DCs for redundancy, sites configuration, users, groups, initial GPOs). There are also licensing and CAL considerations (bare metal and hypervisor, both different), domain and forest options that can paint you into a nasty corner of you're not careful, and a whole host of other things to think about and plan around. I'm not arguing that a domain is bad, on the whole I agree 100%. I just like to set the record straight that building a new production domain isn't as simple as a lot of people would have you believe, and OP might not have the time to go through all that.
I think you're blowing this way out of proportion. It's literally not a substantial amount of extra overhead, it's minimal and for what one would provide in the long run it is worth mentioning.
Tanium has some common apps pre-packaged and regularly updated, you could just setup an ongoing deployment for those to automate keeping them up to date with minimal work on your part.
If you need to update something not on that list, you will need to make an upgrade package yourself with the updated installer or files.
Whether this is actually easy or not really depends on the app vendor and the software. It's usually straight forward, but not always. But that's the case with literally any software deployment solution.
I have one app in particular who's install and config essentially un-automateable. But it's a shitty LOB app that was written in the 90's to be intentionally obtuse to prevent privacy, hopefully that's not an issue in your case.