Not that this really adds a lot, but it at least gives a place for people to vote in favour of discarding graph-algorithms and using algorithms + graphs.
My perspective is that this is the more flexible route. We need a tag for algorithms (of course), and a tag for things-to-do-with-graphs (side note, I still think it's productive to have separate graph-theory and graphs tags, in reference to Kaveh's comment), so graph-algorithms is simply adding a superfluous tag that may make searching harder; someone looking for a graph algorithm has two fairly natural routes via tags using algorithms + graphs, and graph-algorithms could possibly split the group of questions that should be found together.
Anyway, the votes for this answer can help decide.