i don't know why it would be "dicey" considering they just plain were not in recess. and yes, as gregg said, the senate's powers to make it's own rules reigns supreme here.
the second part of the ruling (in regards to recess appointments having to take their positions during the recess) i don't think it's correct. as i've been saying it's about the president being able to make appointments when the congress isn't in session... with travel in the olden days the appointment may have taken some time to get to town. weeks, months, etc etc. and today even people can't just drop everything immediately. i do think that part is incorrect. but is what obama did legal? unquestionably no