the SFTD is there...just not as active in the lobby. doesn't mean they not seeing what's going on and making notes. it means they are not verbally interacting in the lobby.
i've played in a few hot t's and the SFTD has always been present, and not invisible. they always announce their presence (hi eliters or whatever) so we can see they are there. the biggest difference is in the TYPE of chat you might see from them: no spamming for tourneys or eliters, not alot of banter because they usually come from another league to host and aren't familiar with the folks in a particular room.
since they are strictly for premium members, and premium members know the routines, table settings, timer calls, etc, the SFTD isn't really needed to be on top of every word in the lobby, and they can be contacted using the messenger program on the tourney pages if needed to monitor lobby behavior more closely.