By "non-st invites" I assume you mean the minor league players who are not invited to the ML team's spring training facilities, but will show up to spring training later with the minor league team they are assigned to.

You can, but find out what minor league team they are training with, and send c/o that team. I wouldn't send c/o the ML team, if that's what you mean.

hey everybody! i was just putting together my spring training list, and was wondering if you could still write non-st invites c/o the team? Thanks!