I currently use WSUS to handle Microsoft updates on our VM's.
It's OK, but it's not exactly "realtime", plus unless you set it to fully automatic it's a nuisance trying to manually download/install updates on a couple of dozen servers (just the number of logons/logoffs and console sessions gets unmanageable).
I'm tempted to give Update Manager a try, but, for example, I'm unsure how much disk space it needs i.e. does it download all updates regardless, or is it like WSUS in that it scans and then only downloads the updates it needs?
Also how reliable is it?
I guess it's a loaded question but before I install and try it, I'd like to understand the processes involved a little better?
I wouldn't be looking at host updates, just VM updates.
Update Manager downloads patch information at configurable intervals from vmware (for hosts) and Shavlik (for the VM OS and apps). if you choose to install the patch it then downloads it from the applicable site. Once downloaded, the patch is kept indefinetely and will be used again for patching other machines.
There's some good info in the doco for VUM and a white paper on performance:
You definitely should have a try. Not completely sure, but I think that the current version downloads all updates locally. Then you create a basline with specific updates that you need and apply these on you machines. You can do scheduled scan and remediations as well, to take snapshots before remediation automatically, etc. - it's a lot of fun