I don't believe so.
While they do not receive treasure, the ZOOM meeting layout allows for private conversation, so there really isn't any way to prevent this spectator from helping with puzzles.
Additionally, it's just a free walk-through of the puzzles, so someone who is going to run later could effectively get the solutions to everything for an easier run.
True Dungeon doesn't allow spectators to walk with the live groups, nor do they allow the dungeons to be filmed and put up on YouTube, so it certainly seems to suggest that the only people who should have the experience of True Dungeon are the participants.
I clicked on the link I was given for 2A a couple of hours early, thinking that it would just load me into a lobby or queue and I would be online waiting when my meeting popped (basically wanting it in the background while I played some video games, so I'd get an audio clue when it was time to start pre-assemble work). The links turned out to be re-used, so I accidentally popped into an already-under-way dungeon. The host immediately asked me to leave, stating that no one was permitted to join late. I believe he thought I had a ticket to that session and just missed the start time, but he was pretty johnny-on-the-spot about making sure I didn't step into the middle of someone else's run, and that was by accident.
That being said, when I did my run, my daughter did sit beside me and watch the whole thing, and nobody ever asked her to leave or for me to hide my screen. She was even in frame for the camera portions, and actively trying to chime in with ideas for puzzles (although I was using a headset, so only I could hear her). So if you really do want to provide your friend with the chance to witness one without actually playing, invite them physically to your home and let them watch your session play out.
But I highly doubt they are going to permit an additional Zoom guest to hop in and follow along without a ticket.
