Yeah one can. Comparing 25 minute stints in two consecutive years at the exact same position most certainly can be compared. You've got the Sesame Street Bunch on your side, that's it. You can have their wringing endorsement.
No, you can't. Once Finley joined the team it changed the dynamic of the roster. It changed Pop's substitution patterns. If you want to compare Barry's performance prior to Finley joining the team to Barry's performance after Finley joined the team then it is a valid comparison. But you can't compare Barry's 2005 performance to Finley's 2006 performance.
But just to humor you...
2005 playoffs: Brent Barry
13 games/2 starts 23.2 minutes 7.8 pts, 2.5 reb, 1.7 assts, .7 stls, 2.2 fouls
2006 playoffs: Michael Finley
13 games/4 starts 31.6 minutes 10.5 pts, 3.8 reb, 1.4 assts, .6 stls, 1.5 fouls
Looks like Finley was better...more points, more rebs, less fouls.