They did manage to get Reese Olson for Daniel Norris last year, which looks pretty good considering how poor Norris' numbers were. But I don't know if that's a reasonable expectations to get a deal like that again.
The problem I see for the Tigers at the deadline is that, outside of Chafin and Fulmer, you have a lot of veteran guys on this team who would ideally be bait who have horrendous numbers so far, with little indication of much upside on return. And other guys who could be appealing, as you suggest, are bullpen guys like Lange and Vest who, given their age and how long they can be controlled, I have a hard time seeing them getting value that makes the risk of trading them worthwhile.
Maybe if Schoop can go on a tear for a while in July, he could be interesting to teams, but idk, they are in that weird spot where none of the options make a lot of sense.