Ryan,
The UIC coupler on the Mk3 DVT ("82") allows it to be coupled not just to the 90 & 91 but also to any TDM equipped loco (Time Division Multiplex), which includes 86/2, 87, 89 and it has also been used on occasions with 47/7 for Holyhead.
Don't forget also that a TDM equipped HST (the ugly ones with buffers and the big power rack in the old guards compartment) could run with the Mk3 as much as the Mk4.
I must admit that I never saw a 91 with one, but that's not to say it never happened- the Mk4 DVT for the 91 was fundamentally different, albeit similar looking.
One small thing, don't confuse them with the original class 82, (or AL2 (AC Loco 2) as we used to call them)
http://en.wikipedia.org/wiki/BR_Class_82
http://en.wikipedia.org/wiki/Driving_Van_Trailer