There has never been any restriction on running a one-way per the USVTA rules. Certain tracks may have or have had house rules that don't permit them. The reason most people don't run them is that it is hard to come by a track or layout where they actually work better than a spool or diff. What you gain from a one-way is easily lost in the lack of braking on the front wheels when you need it.
Even though I rarely use brakes in VTA, I found that it is the differential action that slows me down in the turns when I lift a little on the throttle. When I've run one-ways (I used to a lot), I've found that natural braking action isn't as effective and I do occasionally want to apply the brakes, which can cause the car to lose rear traction if not done very, very carefully. In this case, I usually use drag brake to do the braking for me rather than risk being inconsistent on the amount of brake being applied. It all boils down to too much work and the car is just easier to drive with a differential.