Okay. Standing Order 119 says a member can, “unless the House or the committee...otherwise orders, take part in the...proceedings”. They can't vote, can't move any motions and can't be part of a quorum, but if the committee concerned says they can, then they can.
Again, I'm at the whim of the committee whether he's allowed to or not, and that's final. That's it. It's up to the committee whether an extra person is allowed to make interventions.