Wow, this thread was work. Not sure the status of what the questions are/were but......
1. When referring to "Pro" players, are we talking indoor or outdoor? Assuming outdoor. And since we're talking, what's even the definition of "pro"? Vice semi-pro? I define "Pro" as someone who gets paid to play and gets paid well enough that they don't have to work at a 2nd job. This may sound like nit picking, but in the US, even today, not a lot of players can make it year round on their soccer salary.
In any event, prior to 1990, there was no MLS. The US had a pile of varied and failed experiments; North American Soccer League, United Soccer League, Southwest Outdoor Soccer League, Western Soccer League, American Soccer League, Western Soccer Alliance, American Professional Soccer League. Just to name a few. I would claim that other than the NASL, the others were semi-pro at best. I'd be surprised if anyone from SC made it to one of them prior to 1990. But maybe so.
In addition to John and Temoc mentioned in a post above, a number of SC players have played in the current USL league with the Battery and other teams. You may consider the Battery semi-pro. A few players probably get paid well enough to live on year round but most do not. Also, their contracts are not for 12 months, they only run for the length of the season. That's probably viewed as semi-pro. To contrast, MLS contracts are for 12 months. (although, try to make ends meet in an MLS city with a full time Developmental Contract that pays you a whopping $20K a year)
SC player Lawrence Smith has played in Jamaica but not on a first team. However, he went to Finland and played for a 2nd division team last year and got picked up by a 1st division team this season. So, he may count in your count, if you're interested in players making it to a 1st division pro team.
