Yes, the answer is yes!
Go to a user's profile URL, then add /tagged/ on the end and then a hashtag without the #. This will show you their posts with that tag, for example:
https://social.growyourown.services/@fedifollows/tagged/art
Now just add .rss to the end of that, so for example:
https://social.growyourown.services/@fedifollows/tagged/art.rss
