Hi Samir,
A developer can easily get this plugin working with Sweetdate or any theme. When I said It did not work, I mean out of the box integration with SweetDate.

The theme already binds popup to register link, so that makes the register link trigger useless for us.

Also, though the homepage registration form looks great on the theme, It is incomplete and can not be used to register user(You see you get redirected to register page on submit). These two make it a difficult combination.

As posted in your thread, I will be looking at it tomorrow( Today, Indian time ) and will ry to find some easy solution.

Thank you
Brajesh