Youtube – Can you subscribe to a YouTube channel as a podcast

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)

I could see a couple of options to accomplish this:

1. You could use Yahoo Pipes to quickly and easily generate a new feed with the combination of the 2 feeds you have already found. No code to write, easy to get started.
2. You could write the code to combine the feeds manually as you suggested. Depending on how you plan to display or use the combined feed, you will want to take care in sorting to interleave the 2 feeds based on dates.
3. You could use the YouTube Data API to request the activity feed for the user. This isn't as easy to try in a browser or RSS reader because you need to have, use, and send a developer key as part of the HTTP request headers in order to get results. Then you will want to filter out activity feed items that are not of interest to you - e.g. when a user subscribes to a channel, comments on a video, etc. According to your question you will just want to grab any entry elements where the category term is marked with 'video_uploaded' or 'video_favorited'. Here is the link to the documentation on using the YouTube activity feeds through the YouTube data APIs: Documentation on YouTube activity feeds