I think Vegeta would have the same advantage over 18 that he did over Zarbon, but with her infinite energy and his G2 strain she would be able to last long enough to win.
In universe it would make no sense at all. Regardless of what Akira Toriyama "felt" like the Super Saiyan boost was I don't think it was ever less than 50x. I don't see anything in the story that keeps it from working either.
If SS4 Vegeta ended up close in power to SS4 Goku after surpassing his limits then it's possible the excess bruits waves from Bulma's machine do give an additional boost.
I noticed it got a lot more hate when I first joined forums compared to now too. I guess Super just set the bar so low that even GT seems decent compared to it.
I don't think Goku's SS4 form got any stronger from the Baby arc to the Shadow Dragons arc and I know some say that Goku's base form wasn't much weaker than his SS4 by the Shadow Dragons arc but I still don't think he'd be strong enough to beat Great Ape Vegeta-Baby.
I'd only put SVB1 marginally above SS Vegetto and I don't think the jump from SVB1 to SVB2 was that large of an increase (nowhere near 8x for sure) so Vegetto would win easily. I'd put him closer to Golden Great Ape Vegeta-Baby.