Thanks for making this poll. I updated it to include a "maybe" answer.
The reason for this is that just submitting your idea to an invention promotion company should not block or prevent you from getting a patent. Most of these companies understand to keep your idea confidential which means that it would not block you from later filing a patent. However, if the invention promotion company is going to start marketing your idea, putting it on the web, etc., then those public activities would indeed prevent or block you from getting a patent so you should make sure you have a patent filed before this happens.
Now, I must also warn people that invention submission companies have a very very low success record so most (99%) of people that spend money with them will never get that money back. Please make sure that the firm you are working with has filed the necessary disclosure statements according to FTC and USPTO guidelines:
http://www.uspto.gov/inventors/scam_prevention/#heading-1