One common question about pagan beliefs is whether or not the practitioner needs to share an ancestral or ethnic link with the system of magick or religion being practiced. In the case of Santa Muerte magick, there's no requirement to be Mexican, Latin American, or Catholic. As the personification of death, the Santa Muerte knows no ethnicity, she has no race, and she waves no flag. Call her what you want and dress her up in any cultural costume you want, beneath it all, she's the same boney lady known around the world. Sure, she might be a rogue Catholic saint venerated by a large community of self identifying Catholics in Mexico, but that's only one part of her story from one part of the world.
Also remember that Santa Muerte is not a creation deity - she's the personification of death itself, and therefore religious neutral. There is not a religion on Earth that does not have a concept of physical death - I would argue that it was death itself which fueled the spread of religion in the first place. After all, without physical death, people would feel little pressure to ever contemplate religion.
Since Santa Muerte magick is not a religion, you can worship any creator - or argue that current evidence does not support a belief in a creator - and still work within the paradigm of Santa Muerte magick.
Ultimately, the working of Santa Muerte magick is not a religion, but a system of low magick for manifesting your desires. It is a system that has grown from the veneration of Santa Muerte, and as I present it here, it's a blend of Mexican, African, Asian, and Catholic folk magick. Why so many influences? Take a walk through any Mexican botanica (spiritual supply shop) and you'll begin to understand.
The botanicas in Mexico don't just sell the stuff you need for Mexican magick, they sell what you need for magick in general. From what I can tell from my own experiences, Mexicans who believe in magick don't tend to discriminate against magick that works, and they've got plenty of systems to choose from when it comes to finding magickal remedies for Earthly problems. In a single Mexican household where magick is practiced, it's very common to see depictions of the Santa Muerte, Jesus, the Orishas, and the Fat Buddha, all occupying their own stations within the home. In Mexico, magick and religion exist independently of one another.
Magick isn't something you're born into or even something you're initiated into, magick simply is. It's accessible by everyone and it comes from plants and stones and amulets and candles and ancestors and prayers and legends and much more - but it sure as hell doesn't come from anybody's permission.