I have the DIYFS donut, and it doesn't smell like donut. Its very dark and just smells semi-sweet and vague. I've yet to mix it, but an older mixer once told me it tastes just like dark vanilla without any 'yeasty/bready' flavor. I'll report here when I get around to mixing it.
Not sure if that was me or not, though the DIYFS Donut does essentially come off as vanilla extract with slightly less alcohol, despite being rather fluid (i.e. it's less viscous than PG and VG). If anything, it comes off as more of the glaze than the donut. The yeasty, bread-like and butter taste would most likely come in with the addition of a cake flavor or two, such as a cupcake or just cake in general, though it'd have to be subtle since donuts are not as dense as cake.
I know FlavorWest has a Cake (Yellow) flavor, as does OneOnOne Flavors. TFA has a vanilla cupcake, though I've not found much use for it personally, though I've also not had the chance to spend a great deal of time with it.
That being said, OneOnOne Flavors also has a Donut flavor. It's not a true Donut IMO, though it is pretty much clear (per the last sample I tested), so you may want to check them out, grab a sample and see what you get from it. I had to mix it at 8-12% to get flavor from it and it is one that can overpowered quite easily.