Hi Mike,
Thanks for checking out our products!
Both our Event Tickets and Event Tickets Plus plugins come with the option to only allow users who are logged in to RSVP.
However, limiting RSVPs to one per user can be done but would require a bit of customization. If you use the Event Tickets plugin, this post provides a great guide on limiting the number of RSVPs (note that this would limit RSVPs per order, but not per user). Limiting RSVPs per user requires more code customization. We do not do customizations at this time but would be happy to help point you in the right direction if you need it. Our Themer’s Guide offers a lot of good info on customizing our plugins.
So the answer to your questions is yes, with some tweaking to limit RSVPs.
I hope that helps – please let me know if you have any more questions!