I agree. Once similar instance I can offer is the Irish placename 'Lugg', which means a hollow. However, I know quite a lot of hills with that in their name and most have Lughnassa celebration links, so a link to Lugh must be there. I haven't worked out where the 'hollow' meaning comes from yet, nor have I found many places with Lug/Lugg in the name that are hollows.

For a great Hagg link look at Agnes in the Scilly Isles.