If you two rough house on a regular basis, and don't hurt each other, then throwing Aikido into the mix likely isn't going to hurt anyone.
Aikido people love to talk about how Aikido is the most gentle martial art in the world enabling you to take down even the most aggressive attacker without hurting them. Then 2 minutes later they'll tell you how Aikido techniques are very likely to dislocate your joints...
Truth is very few Aikidoka ever spar. for the ones that do, first time they spar is usually their last. This because both guys go at it as hard as the possibly can. Throwing all reason and understanding that they are just training out the window. The will both get pretty banged up.
Then they run to sensei who informs them they are not ready for such sparring (cause likely he isn't either). Then they talk about how cool O-sensei was, and that's the end of it.
If you guys are used to sparring, and know how far you can push each other, you are going to be no more unsafe with a few new techniques. In fact, you'll probably find that you can't often use the techniques, then you'll decide they don't work, and you'll be back for a new post that starts like this:
"I can't use Aikido techniques while I spar!"
I've got an answer for that one too, I'll be waiting.
This is the most realistic answer for me. Nice one Chris.
I wonder what's your answer to the latter question?...