We will have to wait until training camp to see a glimpse of the real Bill Walker. If I am right, we will see an extremely hard working, yet raw young talent that is loaded with P.
Bill Walker IMO has all the tools to become a poor man's Paul Pierce. He is very similar to several other power three's in the league. Gerald Wallace, Josh Howard and Matt Harpring all come to mind. Similar builds and skill sets, very strong, tough rebounder, good defender and decent but not spectacular shooter from mid range.
The two issues that are negative and reallys stand out for me are:
1-young and raw without the experience or development of the 3 mentioned, let alone Pierce. He needs to put in some serious time and work to reach the status of the three. Another healthy year at school againts top level competition would have done wonders for Walker, but thats not how the NBA business works anymore.
2-injuries and multiple surgeries are never a good sign and may severly limit his progress.
I will say that regardless of the physical outcome, Bill Walker was well worth the money spent in acquiring him. He will likely end up being another 'so called' steal in the second round for the Boston Celtics. I call this one a no brainer.
Red would have done it in a heart beat. 
He is indeed loaded with P. So much so, in fact, that he had to unload some of his P into a towel during a game once. Search Youtube, I'm sure you can find it.
Anyhow... You mentioned that he will need to put some serious time and work in to reach the status of the 3. I think that's a huge reach, and is somewhat unfair to him. Ray, KG and Pierce were all superstars at one time or another. Even if Walker is absolutely the best he could be, I don't think he will be on that level.
From everything I've seen, there are certain things that Pierce has that sets him apart. He can score from anywhere, he's shown that he can play D as well as nearly any SF in the league, and he has a knack for knocking down absurd how-did-that-go-in shots after the whistle. In all of these respects, I don't think Walker could ever match Paul Pierce.
Walker's strength is a wildcard in this. He could very well end up being an SF version of Leon Powe, in a sense - somebody who bulls to the basket and absorbs fouls like a sponge to water. Add the fact that he already has a decent midrange/outside game, and that could make for a very problematic weapon against many teams (the Lakers, for example).