hardomegersfan What you are asking for would be live demo viewing. There were some experiments that could allow for this to work, but no progress has been made recently.
If you want to be able to spectate players on your own server/hosted match you could write a script adds a chat command that makes the user a spectator.
I actually have a mod that adds such a command, as well as another that prevents you from respawning https://github.com/JezuzLizard/T6-Command-System-For-Private-Match
The usage of the 2 commands would be like this
/spectator name|guid|clientnum|self
and then
/togglerespawn name|guid|clientnum|self
to stop the automatic respawn at the end of the round.
Note this mod will only work on servers or matches you host yourself. There is no way to always be a spectator on a remote server unless the server owner has this or a similar mod installed.