The regular index file should though, so it shouldn't be hard to add that ability to the search..
Of course if you were to just query the index like so (providing you havn't re-coded the query_posts line)..
yoursite.com/?taxonomy=taxonomy_name&term=term_name , you'd get a list of posts that match (if any), so it essentially searches for them..
If you're wanting to search purely for taxonomies and/or terms (and no search word is required), then it wouldn't make any sense to change the search functionality, just send your request (yoursite.com/?taxonomy=taxonomy&term=term etc..) to the index and let it fetch the matching posts for you..
For example i'm not sure many people realise but you can also query for a list of posts in a category using the following..
yoursite.com/?taxonomy=category&term=YOURCATNAME (since categories are also taxonomies)..