I don't have an explanation from a synchronic phonetic perspective.
From a diachronic and phonological perspective, /v/ in many languages, including Danish and Russian, developed from earlier /w/. This is relevant to voicing because /w/ is not a fricative, but an approximant, and other approximants such as /l/, /r/, or nasals like /m, n/ tend to likewise be excluded as triggers of voicing assimilation.
(An unrelated-to-voicing example of how /v/ is distributed in ways that would be expected of /w/ is prothetic /v/ in word-initial position before /o/:
Based on this, I would guess the most likely candidate for something showing similar behavior to /v/ would be another fricative that developed from a non-obstruent consonant. A possible example might be Czech ř or French r [ʁ], although apparently these are not necessarily fricatives (or at least not very strongly fricative) when voiced.