What is NOT okay (at least in the eyes of publishers) is to submit the SAME project to multiple companies at the same time. But IMHO it's a GOOD idea to submit multiple project ideas if you have permission to do so. I know Marvel usually asks that you send EXACTLY ONE project and then wait, but other companies would rather see 100 pitches and then pick the 1 that they can actually use.
I personally will usually wait for whatever feedback is going to come by way of establishing a relationship with a given Editor, but then if things are okay, I'll send more stuff in batches. A company can recognize that you're a decent writer and still not want any of the specific ideas you threw at them.