What do you feel are its strengths? Weaknesses?
I feel the strengths of pro style are its a very balanced attack without sliders you will probably run 20-25 times and throw 25-30 times. The detriments are that it does require actual skill to run it. You have to have a solid QB who can sell the Play Action and a RB who is gashing the defense enough to make it believable. Also even if it requires a great QB it doesn't always make use of that great QB in terms of stat accumulation. For example in a pro-style offense with Wisconsin in 2013 Darrell Murphy averaged a per game statline of 22/33 for 257 Yards and 2 TDs. Erik Wegert in a pro style offense averaged a per game statline of 17/25 for 242 yards 2 TDs. While Wegert in a Vertical offense was 25/40 for 280 yards and 2 TDs... it all depends on what you are looking for and how much you want a QB involved.
Has anyone attempted to use a Hybrid and/or Scrambler with Pro Style? How did it go?
I have never tried this as I have only really run pro style before we got the hybrid designation.
What positions do you think are more important in Pro than others? Do you think a FB is important in Pro Style? Does it use one at all?
The most important positions are easily the QB, RB and the line, I had a 3.5 WR set school records in the pro style so they're less important, if your QB favors them TEs are also really important. They are the ones that sell what I assume is essentially an offense that heavily relies on the play action pass. You need the offensive linemen to be able to pass protect long enough to be able to get off those longer developing PA passes.
As for the combination of run and pass blocking Olinemen I have always subscribed to the school of road graters on the inside and the quick agile guys outside. so my ideal offensive line for this would be Pass/Run/Run/Run/Pass, you can flip one guard and tackle if you want and have a run blocking guard to the side the QB is facing but always a pass blocker on the blindside.
I also prefer a power back in this system for up the middle runs and wearing out a defense. Make that safety really regret coming down to the box