Dan,
Homenet pushes to DDC 3-4 times daily. You can even do a manual push if you want to on the fly. If it was me, I would work on how I could update my Homenet feed from the DMS more than once a day and have DDC to just get the inventory from Homenet.
Are you thinking about discontinuing your service with Homenet and using DDC as the inventory provider to all the third party sites? If that's the case then yes, they have to get the inventory from somewhere (your DMS).
Another thing for you to consider....
Your basically using Excel to set up and structure your pricing, Right?? Why not use Homenets Data Conversion piece. You don't have to download or upload anything. This is a very, very, very strong tool.
You can use it for anything, pricing included. I won't go into too many details about it but trust me, you can definitely use it for pricing if structured the correct way and it's strong as nails. Just call up tech support and get them to help you set up a couple conversions and you'll see.
Did I mention it's Very Strong... 
LOL
Once you use it and learn it, the skys is the limit.
Example: Got some new cars that's been on the ground for a while thats a slow selling color but the manufacture made you order them? Set up a data conversion like this to adjust the pricing on those cars of that color and that color only.
Type = xxxxxx
Year = xxxx
Model = xxxxxxxx
Color = xxxxxxx
Get from MSRP, Subtract or multiply by .xx percentage and put that result in the selling price field of your choice.
There's your conversion. Now every car that matches that specific criteria will get that conversion applied to it. I used color as an example, but you can base it on anything( transmission, trim, drivetrain, mileage, age and the list goes on and on).
