ETA 2: I'm putting this on top because it sort of blows up everything else. Apparently mistaking lethal rounds for beanbag rounds is a thing, as one of the wikipedia sources cites two cases. That's a lot less than the taser/handgun mixup, but on the other hand cops carry shotguns much less than tasers/handguns (being in their car doesn't count). So... yeah. Probably a bad idea. I'll leave the rest of my post unaltered.
I thought that too at first, but further consideration makes me think maybe not.
Police don't use shotguns as a spur of the moment action. Picking up a shotgun is a deliberate, calculated process which is generally not done under extreme time pressure. And by default they're not going to be loaded with taser rounds. So this is probably going to be a high-tech version of those
bean bag rounds.
And that's really what makes me think maybe it's not a problem: I don't hear about cops shooting people with shotguns and then claiming that they thought it was a bean bag round. That doesn't seem to be a thing.
Now maybe that's just because there a lot more cops with tasers than bean bag rounds. Maybe a taser shell would be popular enough to drive up the numbers and reveal a problem. But maybe not. Maybe shotgun usage scenarios are sufficiently different than tasers/handgun usage scenarios that attentional blindness isn't going to be as big a problem with shotguns as it is with tasers/handguns.
ETA: but if I was running a police department, I still wouldn't risk buying taser shotgun rounds. Doesn't seem worth the risk.