Signing draft picks right now is rare and not really a necessity. They can participate in all mini camps and OTAs without having a contract start. They don't need to be under contact really until the beginning of training camp which is in the last week of July. Most of the time you won't see teams start signing draft picks until late June/early July.
However, this regime seems to have a different approach. They went against the trend and actually started signing their picks almost immediately after the draft last season. Not counting Jake Long singing his deal before the draft, the Dolphins kicked off signing their draft picks on May 19th by inking Parmele, Hilliard and Dotson. A few days later they locked up Donald Thomas. Langford signing in early July and guys like Merling and Henne signed just as training camp kicked off(actually, I think Henne missed the morning session of the first day as they finalized his deal).
I would expect they would follow a similar plan and start signing some of the late round picks in the coming weeks and guys like Davis, White and Smith just as TC nears. However, signing them this early is not typical in the NFL.
