Is it OK to put Scott's Hyponex black mulch around my tomatoes

It is a color treated mulch. I'm not in favor of any of these. My vote, use natural.

You should be fine. Just make sure that the mulch doesn't choke the base of the plants.

The website says it's not safe to let the mulch touch other wood surfaces. It doesn't say why. That makes me nervous, probably wouldn't be a good idea to use where you grow food

http://homeguides.sfgate.com/tilling-vs-not-tilling-gardens-76319.html, I prefer wheat straw, cardboard, compost layers to keep seasonal weeds down, and to help retain moisture and keep the soil cool -- black absorbs heat, depending on your 'growzone' that might not be a dood idea-- aside from the chemicals in the dye...

Dyed mulch is not good for anything, let alone a food garden. Shredded leaves are best although they do get tracked into the house rather easily. If you can get some of the chipped tree leavings from a tree trimming company, that works well for pathways in the garden. I've used shredded paper too, and it works great.