X is an android phone. Tapatalk is an android app.
You are going to have a tough time breaking away from that Blackberry thinking. While it is true occasionally some apps will work in one phone and won't in others, the vast majority of them work across the board. Since X will be running 2.1 I see no reason why not.
And more importantly, it has the same resolution screen as the droid. There should be zero problems.