Hello,
If u install umod on your server and u set modded to false, your server will appear on a community server list. Facepunch allow admin tools only to be installed so my question is, is it allowed to use this plugin on a community server? 
Looks like a great admin tool.

this type of plugin is fine for community servers.
it's just common sense, if a plugin modifies the gameplay or adds any UI elements then it is not allowed, that means basically anything that makes your server look modded.

I would be careful with anything using UI, as vanilla servers do not have that. If a player sees it and reports it, your server could be at risk of being blacklisted. Admin tools is primarily what Facepunch allows.

What wulf said.

It is a grey area at best, however, as long as this doesn't affect the players UI, which it shouldn't at all unless you grant them permissions, you should be fine.