Try the attached plugin. Only allows admins that are able to Kick players to spectate T's otherwise only CT's can be spectated.
If the round is not
running it will allow anyone to spectate anyone.
No Commands or CVars.
Keep in mind that if you open the Spectator GUI it will still list T's because that list is build on the client side.
Attached SMX File is compiled with Sourcemod 1.11.
or you could use SourceMod 1.11.6820
will fail because of the DHooks requirement