I'm not sure what licensing issues you are talking about, but setting up a buildbot shouldn't normally run into any.  As long as you have a license to the run the OS, the fact that you are using it to receive jobs from our build master and run them shouldn't be a problem.  You can keep the whole thing behind a firewall in a DMZ: the slave makes outbound connections to pick up its jobs.

On the other hand, the logistics of setting up a cross compile buildbot might be a bit complex, I've never done that.  You might need specific support from our build master.  In any case, the python-buldbots mailing list is the place to talk if you want to/can pursue this.