McCoy is likely just there with the trainers and docs getting treatment; which I believe is the only way players are currently allowed in, aside from contract stuff. Doubt he was there as part of some sort of welcoming committee gesture.
That isn't accurate. You're likely a little confused about this rule:
Workouts cannot begin prior to the first Monday in April for clubs with a new head coach or the third Monday in April for all other clubs
Players are allowed to be here and shake hands with their new head coach if they so choose. Maxx Crosby was at the Raiders facility for their welcoming press conference for Pete Carroll. There's no rule against this.