Deonte Harty is definitely in the mix, but his role is a little unique. People always talk about Taysom Hill being playing that "joker," but that's really Harty. So in terms of being a down-to-down traditional slot, can he do it (will he pop in at the Y, for example)?
Absolutely.
But I don't consider him a traditional slot WR. He does a lot more and the skillset is different. So you're still really talking about two different roles when comparing him and Callaway, even if they both spend some time at the Y.
If Harty stays healthy, his playmaker role is only going to expand. But given his health issues, he's not really the guy you want to consistently use inside to get those 'dirty yards.'