If Slug Bug mosquito/insect repellent is a non-hazardous and non-toxic product it should be alright, but it needs to be used with an anti-siphon/back-flow protection.
Not really. Since the OP spoke of a main line, no antisyphon valve can be used as a master valve. A separate toxic-rated backflow preventer would be required.
Also, it will only take the most minor zone-valve mishap to blow the hose-end device apart, if it is used in a mainline.