Thats like saying, 'if you want to keep that steel deck plate in place, that bolt will work, but as for keeping the whole aircraft carrier together, its meaningless.'
The 'war on drugs' is a multifaceted movement, not only restricted to government or high technology. The 'war on drugs', in its most general and broad definition is the attempt by society to restrict and/or control the usage of 'unnatural' chemical modification of the mind or body - which I believe could be extended as far as overeating (junkfood, which is proven to be more addictive than heroin in mice) and alcohol abuse.
The goal of this hypothetical situation(aquagliders as border patrol, basically), would be to further increase the ability of the nation to control and/or monitor its borders, and stop unwanted elements from entering - theoretically for the good of society through a general consent. Whether or not this is the right course of action is not the point. The US already pisses away billion upon billions of dollars on military operations and technologies that have poor results and sometimes lead to a redistribution of wealth in ways unanticipated by the public. The thought of a nearly real-time global oceanographic reconnaissance system I believe would be too good to pass up for a government who has all the money in the world to do with as it pleases. The interception of illegal marine drug trafficking operations seems like the perfect test bed for this technology.
Im sure that with enough research you can uncover plenty of technologies in use by the US Military in Iraq and Afghanistan that were taken through their initial paces in border patrol capacity.