Just curious as to whether this has ever happened, and if so, what the result was -- spammy answers, or increased engagement and new traffic?
I don't think we've had any hot network questions on Sustainability SE, but I admittedly I'm not sure. The problem is that there is no way to search for questions that were once a hot network question (HNQ) or check if an individual question has been HNQ (feature request for that is on Meta SE).
The only experience I've had with this is when a question I asked on Politics SE became hot (it's this question). I asked it in the morning and received 2 answers. During the day it apparently became a hot network question and it started receiving quite a lot of views and upvotes in a short time. I earned both the 'notable question' and 'good question' badge within a few hours. One more answer was added while it was 'hot' and several comments were made on the answers, but that's about it.