Twitter – List of “used” Twitter hashtags

Twitter Advanced Search has some of what you're looking for -- f'r instance, here's the feed for tweets with the tag '#aardvark' that are emitted by someone named 'pete' (which has no results, sadly)

Unfortunately, there are no wildcards that I'm aware of, so it's an exact-match on the tag and name.

There are a lot of other options available, though.

Perhaps it might be possible to magic-up some google-fu to do this -- and then set up a google-alert for the RSS feed.

Again, I could not find a way to limit it to a specific sender, nor to hashtags (since the "#" is ignored)

You need to create a so called Twitter Bot which will tweet everything containing a certain hashtag.

There is a really good tutorial on this here.