I certainly can't speak for all detachments in the country, but I do know that there are some very busy stations that do have video recording of breathalyzers, which can be very useful in court. They may have videos elsewhere. Parts of these tests take place in a darkened room. I just believe it would cause very serious practical difficulties in stations that have a video set up in one place for one purpose to have to use that particular place for that purpose, for the DRE. I imagine this would cause difficulty on the ground.
Certainly with regard to the issue of seeing how blood pressure is taken--I'm not sure how much that adds to the evidentiary value--or measuring the size of a person's pupils, which are rather important in all of this, I would have difficulty seeing how the video recording would get it all done. I'm certain there will be many places that do not have videos set up in a way that would be compatible with the battery of tests the DRE includes.