Is it safe to use regular craft stencils on cakes or do I need to specifically use cake stencils? 

I have used regular craft ones. I have no idea what they're made of but if they are clean and only been used for caking you should be good to go. The amount of time spent in contact with the cake is very small really for it to be a concern, in my opinion. Others might not agree with me but that's fine by me.

Be careful when you are buying them that they don't have sticky backs - some of the Martha Stewart Crafts ones, for example, are sticky to enable you to use them for fabric and stuff. It would just stick to your fondant and make a mess. 

Thank you so much for your reply. I appreciate you insight.