As mentioned in another thread, work is currently underway as part of the "improved loading of data files that can load from multiple locations in multiple formats" changes to allow WarFoundry to load data files from other applications. The main focus was allowing people to customise the WarFoundry file format (e.g. using binary data instead of XML) but data for other applications is a bonus in the design.
Due to the fact that I've worked with it before and the file formats are simple (INI format rather than XML wrapped in some unknown binary blob that only Army Builder can extract them from) I'll be focussing on Rollcall data loading.
The main limitation I can see in Rollcall is that Rollcall was designed for one game system - old style Warhammer. That isn't a problem, but the fact that it was only designed to run one game system at a time means that it may encounter problems of mixing game systems when used with WarFoundry's multi-path file loading. Unfortunately I can't think of any way around it at the moment other than only including a single directory of Rollcall files in the set of paths to load from.