Yes it is perfectly safe to use both at the same time. In fact it is safe to use any of the grain type fertilizers at any time, day or night, rain or shine, all together or separately. There are no interactions among any of them that we know about. You can use them in amounts up to the smothering the grass stage (more than 50 pounds per 1,000 square feet). You will get some bad odors if you use more than 30 pounds per 1,000 square feet but if you are using corn and corn gluten meal at 10-20 pounds per 1,000 square feet, you should be fine.

Where it might get dicey is if you used blood meal or fresh manure in large quantities. Personally I would never use fresh manure without full composting first. Blood meal is probably best used by mixing it with grains so that no more than 5 pounds per 1,000 square feet of blood meal goes out. Blood meal can get stinky fast and it can burn your grass roots. It is hard to control very light applications of it so mixing it in with something else is a good idea.

thank you for the info!