The Dolphins will lose the roster exemption if they move Eckel to the 53-man active roster, but that's not likely to happen this season.
"We liked him when he was here before," said Coach Nick Saban. "He's athletic, he's quick, he has good hands, he's a good blocker, he's explosive and he is certainly the right type of guy that you want from a toughness and attitude standpoint.
"I think there will be some learning curve for him, getting back into this. Obviously being in the service, he's been working out, but he hasn't been playing football, so we'll try to work him back into it."