Sorry, those aren't star clusters either. They're just regions.
STO treats almost anything called nebula, cluster and expanse as a star cluster with multiple worlds inside (size permitting). That's where I got the idea from.
Well, that's a gross misuse of the term "star cluster" and a reminder of why you shouldn't expect a computer game to be informative about anything resembling reality. A star cluster is a group of closely associated stars, either a globular cluster of tens of thousands to millions of stars gravitationally bound into a spherical clump (usually found in the halo around the galaxy) or an open cluster of young stars formed in the same stellar nursery and not yet dissipated through the galaxy.
By the way, are the Taurus Dark Cloud and the Taurus Reach the same region?
Absolutely not. The Taurus Dark Cloud is a real thing, more properly called the
Taurus Molecular Cloud, a star-formation nebula located near (but not physically associated with) the Pleiades in the constellation Taurus (the Bull in the Zodiac). "Taurus Reach" is a name made up for
Vanguard to refer to the much nearer region in which the series took place, and is called that because it's also in the direction of the constellation Taurus. See, because of how the ancients treated the sky as a sphere and divided it up into constellations, every part of the sky that we think of as a constellation is actually a 3-dimensional wedge beginning at Earth and expanding outward indefinitely, getting wider the farther you get from Earth. So "Taurus" -- or any other constellation name -- doesn't refer to a single place, but to an entire wedge-shaped sector of the sky that expands outward from Earth and has no defined outer limit. In Trek Lit usage, a "[Constellation] Reach" is essentially the name for one of those sectors, or at least the part of it extending beyond the Federation's borders. At least, that's how I've expanded the usage in a few of my works following the precedent of the Taurus Reach (e.g. Cygnus Reach, Scorpius Reach, and Sagittarius Reach).
In
Star Charts terms, the Taurus Reach, or the portion of it featured in
Vanguard, is basically the part of 24th-century Federation space that lies between Cardassian and Tholian territory on the one side and Klingon territory on the other. It's much closer to Earth than the Taurus Dark Cloud.