By all means feel free to use those models in your own armies. The tricky bit is just that since NetEpic uses GW IP it could be a problem if we openly advertise miniatures from other manufacturers in a printed book - even if that book is non-profit for the makers.
I'm a bit iffy about using models that are just stock models form other manufatrurers. Even though there's still an IP issue, I would feel a bit more comfortable if the miniatures displayed are at least a bit converted so they're not instantly recognizable as miniatures from another manufacturer.
That said, I do have my eyes on a few models that could be used - at least temporarily if we cannot find anything scratch built or converted to fit the bill. This has been done in a few other places in the books (but just don't tell anyone

)