I'm not sure it's possible to reverse-dish a 7-speed 135mm-spaced hub - I'd have to look at spokecalc and check, but asymmetrical rims only get you 3-4mm of difference and I think the dish on such a wheel is more than that. But you're right that the specific type of hub does matter somewhat. But using the same length spokes on both sides isn't particularly impressive, since a typically-dished road rear wheel will have 1 or possibly 2mm difference between the spokes anyway, so even without using an asymmetrical rim it's easy to get away with using the same-length spokes.

As I've noted above, I'm using a 7-speed freehub with 126mm spacing that I may bump up to 128. So there's going to be a lot of dish. The rim isn't offset - I highly doubt that there are any offset rims available in the 27" diameter