It saddens me to hear this but I'm not surprised at it, it occurs in our beloved "celtic" music realm and elsewhere too.
Bias takes the form of mere taste to prejudice and bigotry, where we find ourselves in that spectrum is part of life's adventure. Meet intolerance with tolerance as my father would have counselled me, reiterating the words of his father before him. You see, the art of understanding and tolerance is older than the art of music. At some point bluegrass (an upstart music form compared to what I was raised on) was new and fresh and unknown and fighting for recognition.
Traditional bluegrass is not sacrosanct. It seems to me your bass player would make more hay by showcasing his presentaion of the form within an existing jam than by being exclusive, and he would likely reach a wider audience, make more converts, influence more tastes, and gain greater respect.
Bluegrass fundamentalists (like the celtic police) are hard for the general player and listener to appreciate when they'e so doctrinaire. There is a place for preservation, and thank goodness for tune collectors and historians, but music is not static. Music evolves. Music is derivative. It is therefore prudent to acknowledge bluegrass in its past, present, and future forms.
Many of what we commonly call "classical" composers were not accepted in their own day, or at least at the introduction of their style, but today we don't necessarily pay heed to those distinctions. Maybe it's not that much different for bluegrass.