If you have a barn-door van, then yes - the rear bumper (roof spoiler, taillamp (shape) and barn doors) are the same across the T5.1 and the T6.
If you have a tailgate van then no - the bumper profiles are different. However, you can use a T5.1 bumper with a T6 tailgate without issue - all you’ll see is that the profile around the bottom corners of the tailgate is slightly different, as is the shape of the reflectors.
See here:
Difference between barn-door bumper and tailgate bumper?