Hmm, UNC paths are supported. ​Most likely it's still a permissions issue.

https://community.safe.com/s/article/workspace-fails-on-fme-server-when-using-unc-paths

You'll need to make sure the the engines are also running with the correct account​

First, thanks for getting back to me, appreciate it! I had seen the referenced article, but I don't want to change the account for all items, I'm looking more to maybe impersonate a user for this one workspace to run under. FYI, our Network administrator set up FME Server to run under a service account and they don't want to change this.

Hmm, tricky - the best solution is really to have the engine service also run under a service account.​

http://docs.safe.com/fme/html/FME_Server_Documentation/AdminGuide/Running_FME_Server_Engines_Under_Different_Account.htm

I really can't think of another way you could do this. ​

As @virtualcitymatt​ said, the way to get this to work is to have the engines running as the same windows service account as the core and application sever.

I imagine the only way to make seperate workbenches run as seperate accounts would be to implement a distributed FME Server Install with an engine on a seperate machine that is then running as the specified account you want. Then make use of queues to route specific jobs to that other engine.