I am pretty sure that they have other reasons other than just the praying over the animal... because they have to slit the throat in a specific way and if it's not slit correctly then it's not halal.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/islam/1717-is-halal-meat-scientifically-proven-right.html

To my knowledge halal meat was always disallowed in Sikhism as it was wrong to kill an animal to please God or something.