This does not pertain exactly to the D&RG, but to the C&S. The answer to your question is yes, there were passenger cars equipped with both Miller Hooks and link and Pins.
In an internal C&S document dated March 1, 1905, entitled "The Colorado & Southern R'y Passenger Equipment". The following dual-coupler cars are listed.
Baggage 101 - Miller Hook & Link & Pin
Baggage 102 - Miller Hook & Link & Pin
Baggage 103 - Miller Hook & Link & Pin
Baggage 104 - Miller Hook & Link & Pin
Baggage 105 - Miller Hook & Link & Pin
All Cars below listed with Miller Hook on Mail End
Mail & Baggage 110 - Miller Hook & Link & Pin
Mail & Baggage 111 - Miller Hook & Link & Pin
Mail & Baggage 112 - Miller Hook & Link & Pin
Mail & Baggage 114 - Miller Hook & Link & Pin
Mail & Baggage 115 - Miller Hook & Link & Pin
All Cars listed Below, Link & Pin on Bagg End:
Coach & Bagg 120 - Miller Hook & Link & Pin
Coach & Bagg 121 - Miller Hook & Link & Pin
The cars listed below list a "Link & Pin Draw Bar" on the Baggage end
Coach & Bagg 122 - Miller Hook & Link & Pin DB
Coach & Bagg 123 - Miller Hook & Link & Pin DB
Coach & Bagg 124 - Miller Hook & Link & Pin DB
Coach & Bagg 126 - Miller Hook & Link & Pin DB
Coach & Bagg 127 - Miller Hook & Link & Pin DB
Coach & Bagg 128 - Miller Hook & Link & Pin DB
Coach & Bagg 129 - Miller Hook & Link & Pin DB
Coach & Bagg 130 - Miller Hook & Link & Pin DB
The rest of the 3' passenger equipment is all equipped with Miller Hooks, including the open air observation cars.
For those sharp eyed nit-pickers among you, this is before the cars were renumbered.
As for the locomotives, no 3' gauge C&S locomotives during this era show to be equipped with Miller hooks.
Rick Steele