An article in Süddeutsche Zeitung is titled Seehofer ist ein Zocker, kein Hasardeur. According to dict.cc and three other dictionaries, both Zocker and Hasardeur are translated as gambler. To make the title meaningful, however, there must be some difference between the two words. So, what is it?
A Zocker is somebody who gambles. It does not say whether the gambling is particularly risky. It may be implied but not necessarily. There may be the occasional risky ‘all-in!’-bluff, but most of the time they’ll probably know what they’re doing.
A Hasardeur is directly connected to hazard. There is a much larger risk of things not going well for the gambler. To stick with the analogy of above, the risky ‘all-in!’s would be the rule, not the exception.
Thus, the title says something along the lines of
Seehofer is a gambler, but he knows his limits.
The Duden gives two different definitions for Zocker and Hasardeur:
jemand, der verantwortungslos handelt und alles aufs Spiel setzt
jemand, der zockt
And here is the definition for "zocken":
(umgangssprachlich) Glücksspiele machen
(Jargon) (ein [Computer]spiel) spielen
What I gather from that is they are similar, but that Hasardeur is someone who is willing to gamble it all (i.e. go all in) while Zocker is someone who is just reckless and/or careless.