Not sure about the new blood thing – but sounds like a good thing – potentially avoiding the possibility of interbreeding – which must happen. I have never tried releasing any, other than ones who have come from here, but I have often wondered whether the males disperse a bit when they get older anyway. There is a young chap here – 2015 hoglet. Last year to start with he was a regular visitor, but as he got bigger his visits became less frequent and then only occasional. He was back again this year at the beginning of the season, but now, again, his visits are getting less frequent.
Then every now and then a new male turns up. Last year a new one arrived and seems to be still hanging around. Probably too vague to read too much into it, but I do wonder.