I noticed on the Stelladaptor website, that they are claiming that the 2600 paddles will work in Mame32. Of course, we know that Mame32 was renamed sometime back, and is now called MameUI, so I don't know if they are claiming that the stelladaptors will only work with an old version of Mame32 or they just haven't updated their specs page in a good while.
Since we're really only talking about possible use with Warlords here (are there any other 3 or 4 player spinner games?), I don't suppose it would be that big a deal to use an old version of Mame32, in order to be able to use the paddles, unless there's some compatibility issues I'm not thinking about.
Oh, and I forgot that there are actually 2 paddles that are connected to a single controller port, so if I already have 2 spinners on my cab, then in theory, I would only need one stelladaptor to hook up a set of 2 paddles to, in order to play 4 player Warlords. Now I just wonder if the paddles really are compatible with MameUI/Mame32...