In that rare circumstance it would be but, presumably, you wouldn't base or build a relationship on the odd chance that something might happen to cause the one or two instances where you'd butt heads. Picard's and Crusher's authority rarely overlap or conflict, unless there's a medical emergency planetside or shipside which in the grand scheme of things rarely happens when you consider over the course of seven years we only see it happen a handful of times making just a few days.
In the case with Geordi and the Ensign under his command he has to deal with her and manage her every day, all of the time, over specific things as she is under his direct and active control; she can't make a single decision without his input; Crusher can operate virtually autonomously (again, unless there's a shipwide or otherwise major crisis going on.)
Picard dating Crusher could cause some conflict, favoritism and possibly the same situation that occurred with Darren, but the conflict isn't nearly as great as it would have been for Geordi dating a direct subordinate.
In the case with Geordi and the Ensign under his command he has to deal with her and manage her every day, all of the time, over specific things as she is under his direct and active control; she can't make a single decision without his input; Crusher can operate virtually autonomously (again, unless there's a shipwide or otherwise major crisis going on.)
Picard dating Crusher could cause some conflict, favoritism and possibly the same situation that occurred with Darren, but the conflict isn't nearly as great as it would have been for Geordi dating a direct subordinate.