These boards by themselves are not illegal, but loading ROMs onto them is unless you have the legal ROMs from a service such as StarROMs, however, as has been pointed out numerous times, at this point, Namco and Nintendo ROMs are not licensed, so the only legal way to get these games would be to purchase the machines and actually transfer the data from the ROMs to this board, and that doesn't mean by a PCB and toss it in the closet and then download the ROMs from a pirate site.
In answer to the origins of UltraCade.....Our first emulation was of the 6502 and was completed in 1985 running on a Nec V20 CPU. In 1994 we built our first emulated arcade game, Joust. It was followed by Robotron in 1995. As a multi-game platform, UltraCade started out with 8 titles, licensed from Capcom. It is 100% legal and always has been. It's been in production since 1998 and we continue to expand the licensed properites that are shipped on the platform. We have licenses from many manufacturers and have purchased the rights to some games outright.