A business cultivation engineer is basically a sales engineer responsible for interfacing with and being a technical resource for the client's technical buying team (e.g. IT department).
Not really necessary. The distinction between FDEs and product engineers is that the FDE work is focused on a single deployment, whereas a product engineer works on a single product and is once-removed from actual clients.
Where the FDE spends time and what products he works on depends on the client requirements.
This approach really doesn't scale very well but given that the customer base really, really does not like to just take off the shelf software and wants to pay boatloads of money to customize software to their specifications, the software product is just a means to reduce friction and to lower the cost of integration compared to, say, building your own huge data pipeline with open source products from the ground up like oh... DCGS-A and its rebranding as ICITE http://nypost.com/2014/10/27/army-spent-5b-on-failed-technol... https://fcw.com/articles/2015/03/03/icite-faces-resistances....