Since they are purchased as a wargear item and the CODEX doesn't say what are the rules for warhounds in relation to;
1. Counting for outnumbering purposes.
2. Morale checks for cc.
3. Unit size for casualty purposes.

Seems that a wargear item shouldn't cause your lord or AC to break but since they technically are "living" things I'm not sure. With a 5+ save if they could cause a break for an IC I'm not sure they'd be worth it.