But is it not more efficient to blend than to resort to striking?
Well, since the atemi in question was from Daito ryu, the shite would probably be more interested in irimi (entering) as opposed to awase (sometimes translated as blending). There are also styles of aikido that might share that pre-disposition. If you are entering into an attack, atemi can be very usefull in terms of kazushi, taking the opponants space, cutting to the center, and/or causing damage.
Law enforcement / corrections officers face special challenges...they don't like to be filmed overtly striking someone, the people they face can be excessively conditioned, some of them even like to be hit or to feel pain because that enables them to psychologically shutdown and go berserk. Often one or both parties are armed. Things can be very situation specific.
I would not assume (I don't think you are necessarily) that what was taught at the aiki-expo was the sum total of Daito ryu, or that it was targeted to a law enforcement perspective. There are aspects of the art that probably could be adapted very well to law enforcement (that's obvious if you look at the history of Daito ryu), but I doubt that's what the focus would be at an open seminar. It hasn't been at the seminars I've attended.
Your friend is wise to evaluate what he saw in light of his experience and job environment.