I've glued pockets on wetsuits with Aquaseal but haven't had to remove any yet, although I believe it can be done. I only glue around the outside edge which will hopefully facilitate their removal when it's required as well as eliminating/minimising stiffness as mentioned above
Not sure what the construction of the DUI pocket is like, the cordura pockets I have used have a neoprene backing
Personally I like the Highlands pockets, they seem well made with good features at a reasonable price (USD33 with a small tube of Aquaseal included, from wreckdiversupply.com). The backing extends beyond the footprint of the pocket which I think helps with both sewing on and removing
I believe it's common to use a combination of glue and stitching; the DSS website specifically mentions this and that the pockets can be transferred afterwards
If you glue it all over, may be a different story