Robert O'Reilly is easy to spot.
Auberjonois and Shimerman have been around in tv for many years, as has Andy Robinson.
Dorn was Beckett's shrink on Castle
. Watch for him in CHiPs
reruns. My wife never recognizes his face, but always his voice.
Any time I ask her if she recognizes an actor she says maybe. Then she asks if they played a Ferengi.
If you watch much tv you'll see any number of people who have guested on Trek
. Episodic tv tends to cast good people, and they get around.