I worked in casting for commercials and film. We "interviewed" lots of people - a casting session is, essentially, an interview... We'd see 30-40 people per role and (as you say in your question) the problem isn't always with the candidate. We'd regularly get requests for feedback from casting agents so, from the hiring side, I recommend the following:
You say that you're interested in both knowing how the interview went and whether they get the job, so the easiest way to prevent this from being awkward is to let them know in advance that you want to chat about how the interview went and explain why rehashing the interview soon afterwards is important, particularly if they don't get the job, you can strategize for how to improve in future interviews.
Make a "process"
Let them know up front during your preparation session that you'd like to follow up with them about their interview - heck, make it part of the "process". This way they know to expect to hear from you and you can ask when the interview is so that you know when to talk with them. Explain that by talking shortly after the interview, they are more able to accurately reflect on the experience and you want to be there to support them if they have questions regarding "I did ____ during the interview - was that wrong?"
If they outright say that they're not interested in a follow-up, respect that.
Follow up yourself.
On your end, track when the interview is and communicate with them later that day or the following day. If they seem to be avoiding you, don't force communication from them. It's important for you to reach out since you're the one who wants the information. Don't expect them to call you because they may forget, so you'll not be able to help them out further or find out how things went. The longer you wait to contact them, the more likely they will have heard back from the company, so you want to do it within a day or so so that it's before they have an offer letter in hand.
When you chat with them about the interview, ask how they think it went and if they know when they'll hear back about an offer. Let them know that you'd love to hear if they got the job either way so that you can meet up to celebrate - but at this point, as a third party, I don't think you can really expect someone who isn't a friend to keep you updated. If you see them again in the future, you can always ask if they got the job at that point.