Your comment made me want to double check that I had indeed removed everything, which was what I had done initially. But I realized that since JA Enhanced loads mods from it's own folder, I hadn't checked the original Base folder, and lo and behold - the assets from Jedi Outcast were there thanks to running the Outcast campaign mod. That was indeed the case; for some reason, Outcast's datapad.tga and datapad_screen.tga are those weird development textures, and it's a mod I had loaded during both playthroughs.
For anyone in the future, it's under Jedi Outcast's 'assets0.pk3', then 'models/items'. I opened up the pk3 using pakscape, replaced the textures with JA's good ones found in its assets, then repacked. Fixed it right up!
Thanks for the chat, mrwonko. Just verbalizing it a little got the brain gears working to finally find it.
Megakyle's post in Datapad glitch on Courscant; anyone help fix? was marked as the answer