We have two tow bar racks that are designed to tilt far enough to allow the tailgate on most vans to open, we would recommend considering the Atera Strada DL3 (takes up to 4 bikes with the extra bike adapter) or the Atera Genio Pro (takes up to 3 bikes with the extra bike adapter).
The Atera Strada DL3 slides away from the tow ball, allowing much better access to the tailgate than other racks. It has been designed with the VW Transporter and Mercedes Vito in mind.
The Atera Genio Pro has two tilt settings. With the extra low tilt setting you get more space that you need to open a vertical tailgate on a van. This rack is a great option if you are carrying e-bikes,
How much space you have to open your tailgate will depend on exactly which model of tow bar you have and also the type of tow ball and the angle at which it has been fitted. We would recommend having a look at the 'specifications tab' for these bike carriers, where you can find a diagram showing how much space you get. You can then compare this to your van to check if you'll be able to open your tailgate.