This is not an easy question to answer, but certainly a mixed group of criminals existed somewhere: the West is the largest North American region and given all the decades that made up the historic West, one could expect to find just about anything.

The other side of the coin is that any one person can only answer from a limited perspective - because no one knows all the history of the expansive region. I do not know of an example of this sort of gang, and by my experience, the diverse West was also extraordinarily exclusive: emigrants and ethnic groups generally stayed to themselves and despised members of many of the other groups. Just recently I read an account from Virginia City, Nevada of ethnic violence in response to the Franco-Prussian War of 1870: in this case various groups of emigrants allied themselves by religion: Irish and French fought Cornish, Northern Germans, Dutch, and Scots. So here was a case of diverse groups getting together - all in the same of hating other diverse groups. But that's not really what you seek.