Almost any song or tune can be played bluegrass style. The main thing that makes it bluegrass is how the instruments are played. In the old time string bands, they all played in unison all through the piece. In bluegrass, each instrument is featured in a "break" It makes the piece more interesting. Its called Bluegrass simply because Bill Monroe, the originator of this style is from Kentucky.
I too, like Bluegrass, up to a point. But, when they start with "My Martin is louder than your Gibson" I'm gone.
A friend once decsribed bluegrass as sounding like a popsicle stick in a bicycle wheel. It does get that way when they all try to out slam each other and start attcking the instruments instead of playing them.