Simple answer : "Yes"

There are quite a lot of docs on building for Mer ... take a look at:
http://wiki.maemo.org/Mer/Build/Application_Building

It does rely on the OBS to provide the build-dependencies (so I won't claim it's 100% offline) but you don't have to upload the source so no license issues.

Create a package just as you would for a normal application in the url above and when you get to the uploading source section, stop.

Then, assuming you followed along to that point, run:
osc build MerExtrasStable_MerStable_Ubuntu_9.04 armv5el <pkg>.dsc
(I think - "osc repos" will confirm the repo/arch targets you have)

This will actually send the dsc to the OBS and calculate build-depends. Then it creates a chroot and starts a build.

As for the speed, yeah, I noticed !!!

I've made an acceleration suite and my test for it is Qt... that builds at native speed and I run the Qt I built with it on my N800.

Accel : http://wiki.maemo.org/Mer/Build/Cross_Build if you care