There is nothing "questionable" about it, every Metin2 owner does this by keeping track of everything, including every piece of players' hardware.
From what I have read so far, the MySQL data in the GET request is used to install the database (by fetching/executing SQL commands from the OWASP API) after if you change the user and password it will not match anymore with owsap hashed values, by doing this it also works as an license without MySQL there is no running server.
One issue for @ Owsap and not for his customers, however, is that having the license and log in the same place is not ideal.
It allows anyone to spam that URL with GET requests using fake (or even the real one of the customers servers) IPs and other data, rendering it useless for you to read.
You should add an option, enabled by default, that allows users who don’t want to be logged to disable this functionality making the log more transparently and leaving the license doing his job separately or not at all your decision, just an personal point of view.