Learn Dutch: Dronken spelers worden het gokken afgeraden. - Drunk players are advised against gambling.

Because dronken spelers is the subject of this sentence, so the plural verb worden matches it. In an active sentence, the players would be the indirect object (e.g., 'The staff advises gambling against to the players'). While Dutch generally forbids making an indirect object the subject of a passive sentence, a few verbs of advising or requesting like afraden, aanraden, and verzoeken are accepted exceptions. This is exactly what a dative passive is.

Could I make het gokken the subject instead, as standard Dutch grammar usually requires?

Yes, absolutely. You can say Het gokken wordt dronken spelers afgeraden. In that version, het gokken is the singular subject, so you must use the singular verb wordt, while dronken spelers acts as the indirect object. Both structures are correct and commonly used with this specific verb.

Why is the word gokken preceded by het?

Here, the infinitive verb gokken (to gamble) is being used as a noun to mean 'gambling' or 'the act of gambling'. In Dutch, whenever you use a whole infinitive verb as a noun, it automatically becomes a neuter noun and takes the definite article het.

Why is the ge- placed in the middle of afgeraden?