Is swiffer cleaner dangerous to dogs?

No. The article linked below has a good write up about about this, and can be verified on multiple sites on the web.

urbanlegends.about.com/library/bl_swiffer_wetjet.htm

And just to verify from a second and more authoritative source:

aspca.org/pet-care/ask-the-expert/ask-the-expert-poison-control/swiffer-wet-jet-1.html