They do, I have tested it myself.
At one stage I had the complete range of Deben ferret finders and collars so spent some time testing what worked with what. Result were different to that quoted by Deben.
Mk1 finder works with any collar.
Mk1 collar only works with Mk1 finder.
Mk2, Mk3 and Mk3M collars work with any finder.
Mk2, Mk3 and Mk3M finders will work with any collar apart from the Mk1.