Well there are three parts to this library. One is a set of utilities for manipulating audio buffers. Two is a full set of biquad filters, the ones from RBJ: Low Pass, High Pass, Band Pass (constant skirt), Band Pass (constant peak), Band Stop, All Pass, Low Shelf, High Shelf, and Peak/Notch.
The third set of classes is the most interesting. There are prototype classes for each of the common curves: Butterworth, Chebyshev I, Chebyshev II, Elliptic, and Bessel. Then there are a set of pole/zero transformation classes that can take any prototype and turn it into a filter with given specifications. The transformations are: Low Pass, High Pass, Band Pass, and Band Stop. Any filter prototype can be realized by transforming a prototype using a supplied transformation class. To implement the shelving filters, each prototype also comes with a shelving version. Using a single template declaration you can produce pretty much any kind of filter. The filters provided are:
BiquadLowPass, BiquadHighPass, BiquadBandPass1, BiquadBandPass2, BiquadBandStop BiquadAllPass, BiquadLowShelf, BiquadHighShelf, BiquadPeak, ButterLowPass, ButterHighPass, ButterBandPass, ButterBandStop ButterLowShelf, ButterHighShelf, ButterPeak, ChebyILowPass, ChebyIHighPass, ChebyIBandPass, ChebyIBandStop ChebyILowShelf, ChebyIHighShelf, ChebyIPeak, ChebyIILowPass, ChebyIIHighPass, ChebyIIBandPass, ChebyIIBandStop ChebyIILowShelf, ChebyIIHighShelf, ChebyIIPeak, EllipticLowPass, EllipticHighPass, EllipticBandPass, EllipticBandStop, BesselLowPass, BesselHighPass, BesselBandPass, BesselBandStop
So to answer your question, yes you can build a a multiband compressor.