No reason why they couldn't be used regarding the outer planets, but all the information about them I've seen is Traditional. The Modern "equivalent" is midpoint--not the same thing, but similar. Why not give Lots a try, if you have time for it (I do not), and let us know if works for you? You'd have to do some creative thinking for the meanings regarding the Outers. Or if you do find any Modern links, I'd be interested.
Might be a good idea to move your question to the new Modern board to avoid "ruffling any feathers"! And to see if anyone in the Modern category is already using them.
There are several books by modern astrologers which outline new lots often involving the outers; check at Amazon for titles. Both traditional + modernist lots can play a very significant role in chart delineation even if one is applying Purely modernist techniques,