I wouldn't call it lazy. Just unimaginative. At the very most, getting costumes from their other games is sorta like fanservice, since I'm sure there are like tons of Tales fans who fantasizes the idols dancing in said source's outfits. :| And no, not saving their skin, but it does take effort to bring them as DLC idol outfits, so yeah.
I guess what Namco could've done is do some alteration to the costume for other idols. Some of them do NOT match these costumes.