What are these vents in the foundation mortar for?
They appear to be weep hole covers. Weep holes today usually consist of a vertical slot; the result of not putting mortar in a joint. This might have been a retro-fit to address a moisture problem since they are not evenly spaced and are round, which would make sense if holes were drilled in the brick for drainage.

Weep holes are vital to prevent rot of the structural wood framing that's probably on the other side and to minimize moisture inside the brick wall that can freeze and crack the brick in cold climates.

Couldn't find a definitive article with picture but here's more on drainage of brick walls.