I've never heard any width annotated to VFR heli routes. I believe they are meant to be flown as closely as possible.
I do know that in NYC if one is assigned a route the controllers will have a word with you if you fly over the wrong stanchion of, say, the Throgs Neck Bridge. Another example, if one is expected to cross the tower at EWR that does not mean cross the numbers of 04 - that too will get a control a bit talkative.
AIM 9-1-4 para 6 talks about Heli Route Charts but says nothing about width or criteria for use.