Chances are better that the yews will smother other plantings... once they start to regenerate. Yews regenerate from old wood so you can prune out any really dead yew material for cosmetic reasons. I think, though, that it's a little late in the season for any heavy pruning - late winter/early spring is a good time for that. New growth tips can be cut back after the new growth is complete in early summer.

I have a short yew hedge that routinely gets deer chewed when natural food is scarce (Not this year since it was buried under very deep snow) and it bounces back like a trooper. Odd things find their way into this little hedge - forget-me-nots, ferns, Virginia creeper, American elm seedlings. They coexist quite well until I remove them.