No sir. Unless it is a local school system requirement, or perhaps District policy, there is no requirement for an ambulance or even EMS to be on site. The VHSL "suggest" an ambulance be on site for playoff games.
Being a little sarcastic, I guess players in non-playoff games don't rise to the level of needing "suggested" ambulance transportation.
As explained to me, the VHSL leaves it to "the localities ability" to provide said services.