For starters, welcome to TalkBass!
Secondly, you can always just select instant email notification from either "My TalkBass", or at the bottom of a thread/reply to be instantly notified via email when changes to a thread you are interested in take place, regardless of whether you are the Original Poster or not.
As to the actual question, I do not know of any bassists that use a capo, but I am sure you could use one if you wanted to. I'm not sure how beneficial it would be unless you are playing bass chords that include an open string that requires a different tuning, or are playing off of sheets or chord charts that are written for a specific capo position (for example, the charts are written for Capo 2 position, but are written as E, A, B, C# which would really be F#, B, C#, E. I've been there, but it's not too difficult to transpose in my head after getting used to it.). The only question would be, what exactly would be the benefit of using a capo on bass for you, and would you want to use it?
Plain and simple, just because nobody has done it before (or you can't find any specific people who have done it), doesn't mean that you couldn't do it.