The [ɔ] is more o-ish (rounder) than [a], certainly, but it's nowhere close enough to render as "a boat" - the initial vowel is too low and the [ʊ] portion of the diphthong is too high for that approximation to work.
The "aboot" thing did exist at one time in Southern Ontario when, as Stephen Leacock (our Mark Twain) put it: "In Canada we have enough to do keeping up with two spoken languages without trying to invent slang, so we just go right ahead and use English for literature, Scotch for sermons, and American for conversations." The Scots influence was huge in Upper Canada until about the middle of the 20th (and was refreshed by an influx of authentic accents after WW II), and "aboot" wouldn't have been a gross mischaracterisation south of Parry Sound, with Toronto and Windsor excepted.
(Down east, the Scottish influence was more Gaelic then Scots. 25 years ago, it wasn't hard to find Gaelic speakers on Cape Breton whose English was clearly a second language; the kids were mostly English-first by then, though, and Gaelic's little more than a heritage language now. If anything, the Gaelic-influenced pronunciation of "about" and "house" is flatter than the American version.)
