They will include some. DOA5U have 231 free costumes and DOA5LR will have more than 300 for free. Hayashi himself says it.
Now, what costumes do you want for free? I want Legacy and casual costumes. Those are the best
The fact is that if to 231 you add at least 1 never seen outfit for character already included in 5LR disc (there are high chances that they will do something of this kind as already done for 5U) + all the outfits of the basic pack of Marie Rose, Phase-4 and Nyotengu (that currently can't be owned without buying the characters), you reach already the number 282 (231 + 32 + 19).
So or the rest of around 20 costumes will be revealed to be outfit from old packs (as for example Halloween pack or Casuals + Legacy packs), or they will end to be other new outfits assigned only to certain characters (females or exclusive 5LR characters): considering how much TN is saying that all the DLC already bought will be compatible with LR, I see more easily the latter option.
Of course this is just speculation with nothing confirmed and based on the fact that number said by TN is an accurate estimation (more than 300 could also mean "330" for instance, but hardly similar promotional sentences are in a so big defect), but seems to me a very possible scenario.