Can FilterTube block certain creators even from appearing in search results?

Yes.

It does all you have to do is to provide the channel ID.

YouTube serves content from two types of ID UC... and @ Handle based.

You can either paste anyone in the Channel Management section and Filtertube fetches the other alternate ID automatically or you can do it with the 3 dots from the content card and it will automatically fetch and add that channel in the filter list.

and yes you an also activate the Filter All Content label for a channel so any content which mentioned that channels name will be blocked too.

There is one catch if you have added let say "bts" in the keyword filter then on search page you will see the result for @ bts(BANGTAN) why? because if you are interested in a creator but not in other channels which make content about that creator you do not want to see.