Has anyone ever used a packet of dry yeast and a vial of liquid yeast in the same beer to get an appropriate number of yeast cells instead of making a starter?
Yea, it depends on what you're using. US-05 and WY1056 are both the same strain of yeast, so it wouldn't make much difference, but using say, a packet of US05 and a vial of belgian yeast would just be a waste of a vial.
You should really just make a starter with your vial. Brewing can wait a few days.