I think google can crawl flash and read the content. Here is an explanation: httphttp://www.poegames.com/play-1761-Office-Sneak-Out.html If you go to that URL you can see that there is no keyword "mousebreaker" on the page. But if you search "mousebreaker office sneak out" on google.com the site comes 3th in the result and you will see: 2009 Mousebreaker Ltd All rights reserved. Can you sneak out of the office to meet your mates for a pint in the pub - without being seen? Careful! ... "Mousebreaker Ltd All rights reserved." that is in tha flash game.
It totally depends on how the site was constructed but most sites are just a swf file so that's not going to be good. Also like mentioned above if you look at a pages source you'll noticed that most flash sites have like 20 lines of code with no text for google to read some sites don't even take the time to put a title tag.