I would tell them. Dh does not eat beef, or lamb for that matter, fussy git.
There is an expectation of turnkey for Xmas dinner, rightly or wrongly there just is, so I think mentioning it would be a good idea, as for us, it would mean, we could either ask if we could take something already cooked along for dh, or stay at home.
Personally, I would love the beef, I get fed up of bloody chicken all year long.
Although when we hosted Xmas dinner, we did Turkey, Beef and Gammon, which was a pain in the arse.
A lot of people do have a set idea in their head of what their Christmas dinner should be, and as such might well be disappointed if it is not what they have fixed in their head without prior warning.