Are authors of papers okay with receiving questions from people in industry? Would authors of a paper be okay with fielding technical questions about the paper (implementation, theory, etc.) from a person in industry?

I see this as a moral grey area because an engineer in industry is in some way profiting off the work of a researcher without necessarily paying them for the time they took to respond to emails, etc. On the other hand, is the researcher responsible for clarifying details about their paper regardless of who they are being contacted by?

Of course, this will vary from person to person and the length of the engagement, but I was just wondering what the general attitude towards this situation is.
I certainly don't see anything immoral about asking questions.  You may want to mention your affiliation, which will clarify the issue and perhaps also help the author give a more useful response.

The author doesn't have any particular obligation to respond to your questions or anyone else's, but probably will if they are interesting and well thought out.  Academics generally would want to encourage anyone who is interested in their work.

If your questions get very involved, to the point where an academic might consider suggesting a collaboration, you may want to consider offering the author a consultant contract.