MarketPress Combined with Group Deals Cart Plugin

Hi,

I want to use MarketPress because of its multisite, BuddyPress and multi-vendor compatibility. I am also interested,however, in another shopping cart that offers group deal functionality.

Questions:

1. Can I use BOTH MarketPress and this other shopping cart such that:
a. Products/deals are created by this other shopping cart
b. Multi-vendor functionality is handled by MarketPress (vendors can view/edit their own products/deals);
c. Checkout is handled by either MarketPress or this other shopping cart (whichever is the easier integration).

2. If I can use both, what are some things I need to consider in combining two plugins with overlapping shopping cart functionality?

3. If I can't use both together, which is easier:
a. Modify MarketPress to add group deal functionallity, or
b. Modify the other shopping cart to allow for multi-vendor functionality (vendors can view/edit their own deals only)

Thanks.