Rodolphus was more relieved than anything. Relieved that he was not going to have to deal with a howler from home shouting at him about how he could let Rabastan fail so, though all along Rodolphus was pretty positive his little brother would make the team.
He waited till Regulus trotted off before making his way down to his brother. Once he had landed he pulled Rabastan into a brotherly embrace, because he knew it would be the only way he could whisper any kind of warning in his ear. He would have if he could have told him where his clothes were hidden, but Lucius, wisely or not so wisely, kept that from the older Lestrange. He could and however did warn Rabastan "Watch yourself" And as he pulled away motioned to the retreating Black brother. He wasn't sure Rabastan would understand but hopefully when Regulus returned he would.