As far as I know, MAME will not work on an Ultracade cabinet. You can ONLY add the game packs from Ultracade (now Global VR) to the unit, not MAME roms. That was the thing that always bummed me out about them...$2800 for the unit wouldn't be that bad if you could add all the ROMS you wanted to it whenever you wanted too.
However, the advantage of course of an Ultracade is that it is a completely legal, warranteed, backed by a real company, product. There is no "grey area" about the games that you have installed on it, and if you have the rights to play them or not. If you look at Ultracade in comparison to buying all the games, it is great. The problem, for everyone in this hobby of course, is that we are looking at it in camparison to free ROMS.
Ultracade (especially the newest ones) do have a VERY slick menu system. The most recent one I saw, it actually plays videos of the games as you go through the menus, and then when you pick a game, it actually shows you EXACTLY which controls to use, and even uses the sound effects from the game as it displays the controls. I was VERY impressed by this. If this Front End was available to purchase for home MAME machines, I would be willing to pay a pretty large amount for it myself.
Anyway, just my 2 cents...
Brian