As Quan points out in his post, the Aptify e-Business solution interacts with the Aptify AMS directly and you can embed the e-Business controls into Sitefinity pages. We also provide a standard user/role integration between e-Business web users and Sitefinity users.
We do not currently have an integration with the Sitefinity eCommerce functionality that you could use in place of the e-Business shopping cart. I think you have to weigh the pros and cons of building that integration against using what we already provide.
I think the best place to start is to reach out to your Aptify contact and have an in-depth discussion to get a better understanding of what's currently available and how to best design your integration to meet your requirements.
I hope that helps.
Manager, Business Applications at Aptify