cant say anything about hydrogen, but i can tell you that lmms will only support wave and ogg-forbis sound-samples. If you samples are a different format, you can not use them in lmms without a specific plugin - that is btw. true for the GUS samples that utilizes the patman plugin, just to mention one such situation.
So if the samples are specific to hydrogen, you need to run hydrogen in lmms
Wave & and ogg samples are just copied to the samples folders
more here:
http://lmms.sourceforge.net/wiki/index. ... th_Samples
Br.