Quite a few people are running DDPoker 3 under mac OS X 10.10. I personally have it running on 3 Macs ranging from a mid 13 MacBook Air, mid 14 iMac and 2010 Mac Pro under various builds of 10.10, including 10.10.4 build (14E11f) beta without any problems.
Are you able to advise the Modified date of the DDPoker Application you are running? The easiest way is to right click the app, Get Info.
Size: 21,047,450 bytes (25.3 MB on disk)
Where: Macintosh HD / Applications
Created: Sunday, January 11, 2009 at 8:21 PM
Modified: Saturday, April 19, 2014 at 5:19 PM
Version:DD Poker 3
I tried re-downloading and re-installing again, but I still get the "“DD Poker 3.app” is damaged and can’t be opened" message. So I guess I will keep using DD Poker 2.