I think, that asking for "dietary restrictions" or whatever beforehand is not so simple, as there may be cases, which you think are perfectly normal to do and some people think they are totally normal to avoid at any cost, to the point, that they do not consider it as "restriction".
Also the list of what possible would not be welcome will be long or incomplete, probably both (hey, I would not consider to mention I would not like eating live spiders for example ... but I would not eat it)
So I would rather came with something like "I was thinking about ham and eggs and bread for this meeting, would you all like it, or should I came with something else?"
Then it is on the people to either say "yes, good with me" or say "Sorry, I do not eat anything of pigs", "I would not like eat even the eggs, as they are animal babies" or "I cannot eat bread if it contain gluten as I am allergic to it"
So now you see, that the original choise was not best for this group and considering available ingrediences (now and here) you offer something else: "And what about vegetable salad with olive oil?" and now is is all good except the lady there, which say "I would rather get it without oil at all" (as she try to loose some weigtht before season) and you say "yes, no problem, I will not add it on your plate."
Everyone is happy and you know, that you can provide that. And nobody have to solve long puzzles about living spiders, monkeys brains, mushrooms and all other possible foods, which somebody "just does not like" for any personal reason (dislikes, allergy, religion, cultural, whatever).
I will bet, that for ANY food exist at least one person, which does not want to eat it.
Some of my friends are vegans, some of my friends say "it is not food, if there is no meat in it" (and means like at least 75%) ... there are people saying, that doing steaks over "rare" should be punished by law, others like it "really, really well done" (that is just a small step under "totally charcoiled") ...
But usually even in large groups is possible to find small number of subgroups, which would like SOMETHING common for the subgroup and so it is possible prepare like 2-4 kinds of food and make everybody happy.
But IMHO is better to offer, what you can do (have acces to ingredients, have practice with and such) and ask, if it is OK with everyone (and then target the parts, which does not fit), than ask everyone, what he/she/it/... would like (as you end with as much request as are people in the party) or ask what each one does NOT like (as it results to long incomplete lists and feels awkward to many people to talk long about what everything they cannot/do not want eat. But saying "I would prefere salad without oil and just watter instead of beer" is not so hard and is easy to fullfill.)