I have the opportunity to speak to and work with them. I am not employed by Team NINJA or Tecmo Koei though. They do a great job of working with the community and there are quite a few of us here that act as conduits for information to and from TN.
Twitter and Facebook are handled directly by Team NINJA so they'll see it. Just be constructive instead of rude. If it's something more long-winded, you can post it here and someone will pass it along for you.
Well, I was wondering about the Virtua Fighter Jean Kujo, why not consider adding him to the roster? Since Jean is a User of Four forms of Karate, he'd make a great rival for Hitomi. Also, Jean's abilities make him well suited for DOA, Its known Jean Kujo is a new to the VF series and has low popularity. However, It would spark interest if Hitomi and Jean would fight.
That's definitely something you'll want to drop on their Facebook or Twitter. Suggestions like that come in relatively frequently but it doesn't hurt to voice your opinions directly to them.
Thought I should add that in an interview during DOA5 they stated they only wanted VF1 characters to honor the two games' anniversaries. So no characters that were introduced after VF1 were planned to be added.