They don't. They generally teach a fairly standard Gaelic that everyone should understand. I don't think I have met any regional terminology or grammar yet. The only thing we do have is a big range of accents. This is really interesting and useful for the advanced learner (as you will need to understand all of these even to understand what they say on the BBC). But it is a bit confusing for the beginner.
Contrast this with Welsh. They only have one synthetic voice but they deliberately cover a range of dialects, and especially the main standards taught in the North and South. This is incredibly confusing, due to all the wee words that are confusing anyway, and which can vary enormously between dialect.
And no they don't only know standard UK English. We get a somewhat random mixture of three variants, Standard British English, (Lowland) Scottish English and Highland English. The same as on the Welsh course we get a mixture of SBE and Wenglish. In both courses, they generally add common standard American variants when they are drawn to their attention, but they clearly cannot include all regional variants, and nor can they be expected to be fluent in American English by themselves.