Does a witch have to make a check vs a creature with SR, when using slumber. I know they don't normally but the phrase "as per the spell sleep" makes me think it should. Since the spell sleep does apply SR.
No. Supernatural abilities are not subject to SR.
When in doubt, remember that SR means spell resistance and you are good to go.
Only spells and spell like abilities are affected by SR.
There is a chart that shows what affects what type of special abilities.