I towed from 2008 to well into 2016 with a car fitted with dual 7 pin sockets, and the ATC worked faultlessly, so they certainly can work with 7 pin setups.
It might require you uprate the car's fuse feeding the maintained supply positive pin; the addition of the ATC's draw, under certain circumstances, "can" take out the 15Amp fuse typically used in installations.
Mine I changed to a 20Amp fuse* and have never had that blow.
* I sought and received the car makers approval to uprate to 20 Amps but only for specifically use in this case.
When coupling up the plug to the car you might well hear the ATC operate, going through its checking procedure; ensure if this happens that the ATC's LED [if featured] does not "Flash" Red. If it is not then the ATC is either not functioning or otherwise leaving the van in a safe state to tow.
[Flashing red basically means the ATC actuator is not safely in the "home" position, inferring it might be partially or fully applying the level of brake application it can. In that state you can't tow without further intervention]