I've made the alliance selections at all of the regular-season events and most of the off-season events for our team since 2007, so 3+ years of experience... I have never been on the drive team or designated the team captain, and never had any problem with it. I would suggest never having the alliance selector be anyone but a scout. Most drive team members or alliance captains have not been watching robots the entire day... I would also strongly recommend having the pick-list maker a scout who goes down to represent the team. Anyway, I'll hold back on my person "do's and don't's" of scouting...
FIRST truly does not care who makes the picks as long as it's a pre-college representative of the team. Whether the student is the "team captain" or is a member of the drive team is irrelevant. Hope this helps you!