[Ulzgoroth]

Per 5.11.3, infantry may not dismount from a vehicle the same turn as it embarks.

It's not specifically noted, but it seems to follow that that would include dismounting for an overrun per 8.06.1. Is this correct?

This led me to the question: what happens to infantry if their mount rams or is rammed?

Being rammed by a GEV is treated as an attack, so it would fall under the usual rules for attacking a vehicle with riders. But armor carrying infantry can also be rammed and instantly killed by Ogres, or suicidally ram Ogres. Infantry can also potentially ride on rule 13.07 superheavies or Ogres.