Hi Shamir
The Grasehotspot package isn't yet designed for hosting in the cloud with dd-wrt. There are plans in the future to support that. Currently, it's designed to be installed on the router, or a computer on site.
There are other hotspot packages out there designed for what you are doing. If you are familiar with Radius and Coova Chilli (Chillispot), then you can indeed connect dd-wrt to a Grase Hotspot server, however I don't currently have instructions for this as I don't have time to invest in writing a howto on this. If you do want to work it out, we can certainly help on the mailing list, and then publish your results on the wiki.
Regards
Tim