I know that this reply is well out of date and that you will have planned your workshop by now, but I would agree that if security etc. is important then Moodle Quizzes are a good way to go. However, Hot Pot is very easy to use and I have found that teaching students how to author it is a great way to encourage them to spend time working on grammar specifics. The JMix module is also extremely good for encouraging students to develop the idea of 'chunking' language as a reading strategy.
If you could combine the two via an introduction to Moodle and its CMS/VLE aspects, a quick look at Lessons and an overview of the Quiz settings before a short intro to Hot pot, you would be giving your delegates a great idea of several possibilities. Hotpot does have a really good tutorial which would allow people to develop the exercises on their own. Uploading to a site is not that difficult and, in many places, not something which teachers actually have to do.
I think that, if it's possible, let people gain a little exposure to both.
Phil