But, other Scottish people certainly don't have trouble with understanding a Scottish accent. So I view that as a certificate that we should be able to build a speech recognizer which can recognize Scottish accents.
As a Scottish person, I'll say there's a huge amount of variation between Scots dialects. As someone who grew up in Fife, it took me well over a year of living in Glasgow to be able to reliably understand people there—and both of them are typically classed as Central Scots.
I also grew up in Fife, although my parents paid good money so I would have an Edinburgh accent. Glasgow was like a foreign country to us...
I grew up in St Andrews, both of my parents having grown up in England, and went through speech therapy as a young child (due to dyspraxia); unsurprisingly, with that, you can imagine my accent is much closer to RP than any broad Fife accent, though most of my speech is definitely Standard Scottish English.
Whether or not gathering a sufficiently large corpus of other dialects will solve the problem would be interesting; also it might be uneconomical to gather a large enough corpus of some dialects, leaving minorities out.