I don't think underestimating the Shivans was even avoidable.
However I'm going to come down on the side of what Command ordered in Playing Judas being probably stupid. They took a risk, to be sure, calculated, but it's not the wise sort of risk. As Heinlein once said, "Men are not potatos." It is very important for those in the military to believe that it actually does care about them as individuals, that it will not risk their lives without purpose, and most especially, that it will not send them into something they have no chance of surviving. One might regard it as a semantic distinction that a good officer never orders a man to his death directly, but to those who might actually be ordered, it is a very important semantic distinction.
Command directly ordered you to your death. This is not the action of a wise officer. (Particularly considering Alpha 1 is rapidly proving to be the most valuable flight officer aboard his destroyer! His death could have extreme ramifications for the morale and discipline of the Galatea's aerospace group, never mind the obvious loss of your most effective pilot!) Moreover, whatever they hoped to gain from it is deeply questionable. We have to assume that Shivans would have considered the obvious weakness a flight/hanger deck causes in a ship's design. To again quote Heinlein "Any race that can design a spacecraft is not stupid." The effort to order you into the hanger might have provided all kinds of fascinating information, but it's doubtful it would have revealed any key design weaknesses when the Shivans went to such trouble to design the Lucifer as an invincible craft. Even if it had, we have no reason to believe Alpha 1 could have actually transmitted his information from the hanger.