Of the 8, Alberto Castillo and Travis Hughes have the best chance of making the ML club when camp breaks. Castillo is a defensive-minded catcher while Hughes is a possible bullpen piece.
The other 6 represent organizational depth, pure and simple. Bailey spent last season in Pawtucket. Jimenez at Portland. Both are possible options should either Youkilis or Lowell get injured/falter.
Joe "Not Joltin Anything" McEwing is the perfect example of organizational depth, minor league leadership, and something I call: scrappylicious. Not sure when/if he'd ever crack the big league roster this season. What can I say about the others? Rogers is a prolific hitter (career .207 BA!), Kerry Robinson has been given his walking papers from such notable organizations as the Tampa Bay Devil Rays and the Kansas City Royals. Scales will probably end up behind McEwing on the minor league backup infielders list, but has actually had pretty good OBP numbers over his mL career.
In case you missed it, all are non-roster invitees.