WireGuard is unique in that it's deliberately coded as 'just another (unix) network interface'. You can literally make it do anything you like - policy based routing, source/destination based routing, per-client routing... Whether Untangle expose that in a GUI is, of course, another matter. I think they have a cheek charging $150 a year for not disabling access to a completely FOSS project with less than 2k lines of code, though!