That depends if it's the azimuth part of the TACAN that's u/s, or the DME part, or the whole thing. Co-located requires certain proximity requirements to be met (or they're not considered co-located). If met, then a VOR positioned near enough to a TACAN is co-located with the DME part of the TACAN installation, and can be considered to be a VOR/DME as far as civil flying is concerned.