Is removing network access to a shared Time Machine drive mid-backup similar to unplugging a physical drive?
The nature of backups is that you have an hourly window of time to start one, so the majority of the time, the majority of the computers are not mounting the network share. The algorithm itself is solid in my experience. 

If you are starting the first backup, that can take quite a while to save, but if you corrupt the disk image then, you can nuke it and start over with no loss of data (there weren't any backups to lose).

The OS enables journaling so that the worst that happens in practice is the one interval that was in the middle of being changed gets cancelled and cleaned up. I've had very few OS X server backups have issues with network backups, so as long as the software you run on the NAS is equivalent to OS X implementation you should be just fine with your plan. You can also hedge your bets with periodic backups to hard drives. OS X supports multiple time machine destinations as well as ad-hoc adding and removing them to make more point in time ones that you can archive easier than trolling for changes on the NAS.

Some data points - roughly 100 Mac are backing up to about a dozen Mac Mini over the last 3 years, and the number of trouble tickets to assist with things users can't solve has been 2. One user was able to be guided to mount the backup destination and use Finder to remove the partial backup interval. The other made requested we copy their image to a hard drive from the server so they could get the files they needed. That user used a local HD to do backups in the interim and now backs up to that drive and had us wipe the server side image and is backing up to both destinations with no issues.

We don't manage anything or train users to do anything special. Power off, disconnect from network, they just expect Time Machine to run and we train them to check on it two times: a) before making a large change to a document that losing work would mean losing more than 4 hours of work. b) once a month, run a backup manually from the Menu Bar to ensure it completes.

On the server side, we have visibility into when backup images are not updating for more than 3 weeks by a script, so you can implement a check on your NAS if you desire to recreate that Server.app functionality. For $20 I'm a big fan of using server.app to handle things, but lots of people like DIY too.