I am not grossed out at all by the dad and son kissing on the lips or even sharing a bed...and I think you are being too critical about these things. You don't ever kiss your kids on the mouth?
As far as the ringworm is concerned...kids can get ringworm from playing in the dirt, so that doesn't seem to be an calling CPS issue either.
As far as going to work with daddy, you say he is stocking shelves and it is a retail store, I doubt the store would pose any danger to him. I think that the fact that dad and son are spending quality time with each other rather than dad just dropping him off at a sitter is pretty cool, and possibly even fun for your son...quality father/son time! If he is going on appointments with his dad to do the actual spraying of chemicals at the 2nd job, I would suggest asking that he not come in contact with anything dangerous to him, that is a reasonable request. Do you think his dad is really exposing him to harmful chemicals? If so, by all means speak with him and let him hear your concerns...they are absolutely legitimate and should be talked about.
The only thing you said that would truly worry me would be the riding w/out a seatbelt. The dad should know better than that!
I can understand your worrying about your son...but the part that bothered me about your post is when you state that "the straw that broke the camels back" about your ex kissing your son? I am confused by this? I know this man is your ex and you might be harboring bad feelings about him but please keep in mind that this man (more importantly) is your son's father! The relationship they have is very important to your son's well being...I would think long and hard before doing anything you might regret later.
Best of luck to you...its hard being the mommy sometimes...all the worrying and such!