Are authors of papers okay with receiving questions from people in industry?

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.

This is not a moral grey area - asking is totally okay.

In my country (Germany) researchers at public research institutions are even expected to answer. It's called "third mission" (the first two being research and teaching respectively).

Besides this "third mission" I shall pursue (helping to bring their research to industry), I would be pleased to learn how my research would be helpful in practice and would love to help the company. Just explaining some details is no problem at all. If this develops into some severe counselling one could start thinking about payment, but actually, this is often how collaborations between universities and companies start.

There’s a distinction between asking an author for clarifications on what she/he has done and asking said author to do more work. The former is fine. The latter... well... I wouldn’t assume an author would necessarily do it unless this extra work would be of some benefit - v.g. additional publication - to said author.