Here's the good news on Hunter Harvey. The Nationals are quite bad and will remain so for a while, so his availability shouldn’t be a problem. He's also putting up some decent surface-level results in 2023 with a nice strikeout rate, he throws hard (which helps the cause, and has two years of control left after this season, so he could be around for a while.
However, a cursory look at his advanced metrics shows signs of potential trouble. His walk rate, whiff rate, and chase rate are rather meh, and the amount of hard contact he gives up is downright alarming. That said, the Dodgers are really good at getting the most out of their guys and there is a decent chance that they could have some adjustments in mind to quell some of those concerns. If that's the case, he won't be particularly cheap in a trade as the Nationals need to stock up on talent and will probably value Harvey’s team control highly.
Alexis Diaz: The pipedream
Alexis Diaz is the sexiest name on the hypothetical trade market when it comes to relievers, and for good reason. Sure, he has walked too many guys this season, but the stuff is absolutely electric and everything else about his profile is very exciting. That fastball/slider combo has the chance to be very good for a long time and he's under team control through the 2027 season.
Whether or not the Reds would even entertain trading Diaz is a fair question. They are an improving young team in a bad division, so trading away their hotshot star reliever that has tons of team control may not go over well and may not even be a good idea. However, relievers are still relievers and almost all of them are on borrowed time. If the Dodgers were able to come up with a big-time trade package that maybe included a player that could help the Reds this season, that might be enough to convince Cincinnati. That said, don’t think that most of the rest of the league isn’t trying to find a way to pry Alexis out of the Reds’ hands, too.