I'd rather broadcast seed and fertilizer seperately for a few reasons.

I'm not sure if the fertilizer will hurt the seed coatings or not, but why take a chance?

You do NOT want to disk in seeds as small as you are working with. It would much better to broadcast and leave it on top of the ground with no packing or dragging than disking them in more than 1/4" deep. More than 1/2" deep and you probably will never get them out of the ground.

Disking in the fertilizer is great. Just do the seed on a different run.