GoRatings lists 892 active professionals with at least one game on Go4Go. Wikidata records 951 total people with "Go professional" as their occupation. Sensei's Library apparently has entries for over 2,000 total professionals, which surprised me.

Do we have other statistics? From GoGoD?

The GoGoD Onomasticon has over 4,500 entries. Some are for journalists, poets, amateurs, shoguns etc but nearly all are for pros or equivalents (e.g. guoshous) spanning nearly 2,000 years.

Wow, that's a lot!

The Japanese rank progression page has 908 names. My collection of (mainly Japanese) pro go game records has 3582 distinct names (where different names sometimes belong to the same player).