Spell Check only lower case words?

Probably won't help you, but assigning No Language to names would cause Spell Check to skip them.

ID's spell checker is on the primitive basic side. It doesn't even have the common "skip uppercase words" or "skip words with numbers" filters, much less anything as selective as what you ask.

It's possible there's a script workaround, but my practice is to make sure large documents are fully proofed in Word before importing into ID. (Not just spelling, but technical glitches like multiple whitespaces and other details.) That's not always possible—not all docs start in something like Word—and it won't catch typoes or goofs added during formatting. But ID never has been an ideal tool for document (content) development and editing.