I just ran into the similar problem, but the resolution was different :
In gitolite3, it seems that if you simply see a gitweb.* property, then your repository is gitweb enabled:
repo foobar
desc = "Foobar repository"
category = "foobar"
Rw+= myself
Or if you prefer :
repo foobar
config gitweb.description = "Foobar repository"
config gitweb.category = "foobar"
Rw+= myself
I don't know if it works with a @all, like:
repo @all
category= "uncategorized"
But since a description or (valid) category is not a bad thing to have, I'd say it works for me.
On the other hand, I tried also making an @almost-all group with all my repositories except gitolite-admin, except I don't know if it works because of gitweb.description/category config.