Two suggestions:
1) At this age, transitions are very hard for kids. When your husband arrives at daycare, he should say, "Susie, in 5 minutes we will go home. Start saying goodbye to your friends." (And then a quick reminder at 2 minutes.) When the 5 minutes are up (this should give your husband enough time to pick up little Susie's things and sign her out), he says, "Okay, Susie, the 5 minutes are up! It's time to go!" And then he walks out the door. That 5 minute warning will give her enough time to pull herself together and make the transition between playing with friends and going home. Sudden transitions can be very frustrating to a child this age; it makes them feel like they have zero control in their world, and someone is just swooping in and making things happen that the little person didn't know were going to happen.
2) If she hits, Daddy makes the whole world come to a screeching halt, however he wants to do that. My husband is a big Italian guy, very loud under normal circumstances. But when one of our kids has done something really bad? Oh man, all hell breaks loose. He is LOUD. Gets right down to their level and just reads them the riot act. And believe me, the child definitely thinks twice before performing that action again! Is that the way I'd handle it myself? No. But at that moment, he's the one interacting with the child, not me. So... Daddy is in charge of what happens there.
A final note: at this age, kids have no concept of "When we get home, you're having a time-out!" Pretty much, the discipline needs to happen then and there, or it doesn't make any sense to the child. So if she hits him, he needs to handle it right then, swiftly and memorably, so she realizes that's not something she wants to do, ever again.