Can one actually use the sights on those pistols
to any degree of accuracy?
If you are talking about the GI type peepsights, and holding the gun the way one normally holds a handgun (at arms length) the answer is effectively, NO.
First off, let me say that my opinions about the AR pistol (and any of the other "handguns" that are essentially a chopped rifle or SMG design) have NOTHING to do with our right to own what we want, like, or enjoy.
I've had, or had shooting experience with a number of these kinds of pistols (although I will admit, not the AR pistol specifically), and I've done my share of "one handing" the M16.
Cobray (Mac), Tec-9, Uzi, HK, Tommygun, AR, AK, and all the others in this general group of handguns are all less efficient for practical purposes than other designs. Where they excel is giving us the enjoyment of owning them, as the closest thing to their design ancestors as allowed under US law.
I was thinking of discussing the details here, but I think that question deserves its own thread.