Whichever sampler the author created the libraries will have its own formatting system, and may load or not in other samplers. EXS, Nki, sfz, decentsampler and so on, may not be able to be loaded in many samplers but the samples often can be.
Any sampler that can import multiple samples, and has some form of sample mapping (and hopefully editing tools) can be used to create instruments from the type of samples that it can load.
The majority of samples with libraries on Pianobook are .wav or aif format and will probably load into Halion.
You could import a whole folder of samples and use whatever mapping is available or manually create an instrument from the samples. Or you could drag a single sample across the whole keyboard and create something.
The result may not be as the original creator offered, but does it work for you ? Or can you use the tools you have to improve it ? Or should it be deleted; right now!