Here's one idea about oompah bands :
In some bands (no violins or drums) the base line was carried by the bassoon (that big bell instrument the player "wears" - have I recalled the right name musick?) which has the sound ompah-pah. It made for a distinctive collective sound. Hence oompahpah bands.
The same 3/4 tunes could be played by other groups of musicians from bands with drums to full orchestras.
Well, anyway it's a place to start the ideas, right?