Can PassagePoint be accessed via VPN?

Since VPN is transparent and works at the network layer, PassagePoint wouldn't know that it's on a VPN, so technically, it would work.

However, this largely depends on the VPN reliability and network bandwidth. VPN encrypts traffic in both directions over an already slow and unreliable network (internet), so in general, the result is slow and unreliable.

It is not recommended to run PassagePoint over a VPN.  If you plan on running PassagePoint over a VPN, you should fully test it in the environment to make sure they are ok with it the speed and reliability.