Is Santeria a sin in the Catholic faith?

Please be 100% sure

Yes. The religion does incorporate some traditions "borrowed" from Catholicism, as well as several other religions, but their teaching is clearly opposed to the core beliefs of Christianity, and therefore Catholicism.

Yes. Santeria is a mix of the Yoruba religion and Roman Catholicism.
They disguise their 'Krisha's' as Catholic saints and worship them.

Yep. It's considered the practice of another religion.

I had an understanding of this Santeria as being like voodoo. I read about it in one of Nicky Cruz' books. He said that they have given demons the names of the Saints from Catholic religion.
here is the link I found on line for you to read up on it.
http://www.wisegeek.com/what-is-santeria.htm