That’s exactly what the VIA offers. It has hardware encryption acceleration. But better than being on a separate card, it is built into the CPU.
This has a lot of performance advantages over an add-on card. You can see this in the benchmark results vs. the Pentium D.
The VIA chip was designed for exactly this kind of use. In an embedded VPN router application.
I can confirm that enabling it not only improves encryption speeds, but lowers overall CPU usage.