https://community.bistudio.com/wiki/orderGetIn and https://community.bistudio.com/wiki/allowGetIn are persistent states for a group, if the given group can use (assigned/added) vehicles.
However without getter commands, its very tricky to use them reliably. Even more so, as the engine itself uses these states and modifies them internally as well.

Overall making AI use vehicles via SQF is complex and tricky - these getter's would make the situation at least more manageable.