IMO, teams should keep as much flexibility as possible. Sometimes that means putting a guy on the big league roster mainly because he is out of options until the team can better gauge exactly what they have in that player.
For that reason, I hope that Swihart, Brentz, and Marrero do have an inside track. I don't think that any of them will necessarily outperform some of our other options, but the possibility exists that they might.
All that said, I'm pretty sure that Holt will be on the 25 man roster, despite having an option remaining.