This is kind of a feature request, since it doesn’t exist and is not a bug.
When I was working on my game which is going to support controllers (for hopefully Xbox One compatibility), I found this out the hard way. Turns out ROBLOX does not Dualshock 4 controller as having compatible vibrators. No idea is this is because they are checking in the wrong spot, or it just hasn’t been added in yet. After I found this out, I decided to connect via USB instead of Bluetooth, still didn’t work.
Anyways, support for Dualshock 4 controllers being able to access vibrations would be amazing. (Maybe it’s already being worked on for ROBLOX for PS4? :D)