I think Sage is saying don't run Sage 100 through a VPN without also using a remote desktop type solution - TS or Citrix. I have a current 2017.1 Advanced with 6 users where a couple users ran Sage via VPN without RDP and did not appear to suffer ill effects. I recommended against it and recommended only using an RDP type solution for remote workers.
Eventually, they went with RDP. Until they did the remote users coming in on VPN has the type complaints you would expect - very slow Crystal Reports, register printing. Overall the speed wasn't as good as an RDP type solution but I don't think we ran into any major issues (speed aside).
About 1/3 to 1/2 of larger customers in secure environments require me to use a VPN with RDP and I've never seen any type issue combining the two. I think using VPN only is the problem.