Up until recently I never had a problem with the Flash player with any of the G4s (PPC). But now even after updating it they still say that the Flash player is out of date. Well they are not supporting the older Macs. Even if you are running 10.5.8.
So I went looking around and was hearing the same thing. They I found a person who on his own redid a flash player so that Flash would work on the PPC. Now stuff that would not normally play did. It also worked with G4 PPC that were running 10.4. I have not yet tested them on the games that require it as I do not play the on line games. But I kind of think it will work. What I find a bit strange that it is smaller than the Flash plug in it replaces.
Also I am kind of wondering about the security issue's since you are replacing something with something else in OS. Seems to have no problems with anything so far, or any weird things going on in the back ground.
Link please? As long as you are cautious then security should be fine, however I have heard that Flashback Trojan may be able to infect PowerPC Macs. Not totally sure but if it works then use it.