"Many" may be a stretch, but at least a few of the actors did meet that description, if only in bit parts/cameos.

I think the only actor to that description that played a 'major' role on the show was the one who played Snoop: https://en.wikipedia.org/wiki/Felicia_Pearson

Besides Felicia "Snoop," Pearson, here's a partial list of main characters that also meet the description:

https://en.wikipedia.org/wiki/Donnie_Andrews

https://en.wikipedia.org/wiki/Melvin_Williams_(actor)

https://en.wikipedia.org/wiki/Ed_Norris

https://en.wikipedia.org/wiki/Gary_D%27Addario

https://en.wikipedia.org/wiki/Jay_Landsman

https://en.wikipedia.org/wiki/Richard_Burton_(Baltimore)

https://en.wikipedia.org/wiki/Steve_Earle

https://en.wikipedia.org/wiki/William_F._Zorzi

https://en.wikipedia.org/wiki/Anwan_Glover

And don't forget the show's creators:

https://en.wikipedia.org/wiki/David_Simon - former journalist at the Baltimore Sun.

https://en.wikipedia.org/wiki/Ed_Burns - former Baltimore police and public school teacher.

Would you be surprised if I told you that you can be both an 'actual former gang members, police officers, judges, politicians, teachers, etc' and simultaneously a 'professional actor'?

What I mean is that they were hired based on their acting CV and auditions. It turns out that a very small number of mostly minor actors had some run in with the law in their youth, and there is one actor who had been selling drugs decades before. This story got media play when The Wire was on TV and people thought that the producers had gone out and hired actual gang members for the cast. This isn’t true. They went through the usual screen actors guild and casting process. The iconic characters people remember are mostly stage actors, and not from Baltimore (two of the main characters are British).

Felicia Pearson was in prison for murder...

She’s the one I was alluding to.

Steve Earl, who plays Walton and performs the season 5 theme, is a professional musician but also, like his character, had trouble with heroin.

https://en.wikipedia.org/wiki/Steve_Earle

Or https://en.wikipedia.org/wiki/Melvin_Williams_(actor)

the guy who plays the deacon on the wire was a drug kingpin back in the 70s/80s. he was actually arrested by one of the writers of the show.

Melvin Williams

as posted above: https://news.ycombinator.com/item?id=25626484

In addition to Snoop, the actual Jay Landsman (real person) plays a sergeant in the wire, though it's a small part and he does not play Jay Landsman (the character).

Additionally, the actor who plays detective Ed Norris is the former police commissioner for Baltimore and the former Police Superintendent for the state of Maryland.