Someone who practices Voodoo or Santeria may sometimes tell a non-Voodoo/Santeria person that they pray to the same saints as a Catholic does. But my Santeria-practicing friend informed me that it's actually very different. The religion began in west Africa and when they came over as slaves to the New World, Catholic priests & nuns basically outlawed their native religion from back home. So they quickly figured out that it would be easier to assign each of their 'saints' from voodoo/Santeria to a Catholic saint.
But no...they are not the same. When a Santero prays to one of their saints, he is praying to an orisha. So, for example, when a Santero prays to Our Lady of Mercy, he's actually praying to Obatala...very different. When a Santero/Santera is praying to & lighting a candle of Saint Peter, he/she is actually praying to Ogun. Each orisha has different strengths & weaknesses.
Many Santeria ceremonies are spoken in the Yoruba language...that and Spanish. But when they're calling upon their saints, they do it in Yoruba.