Obama as a constitutional law professor must know this, and he probably knows how it has been evaded in the past (by Nixon, Carter, and Clinton) - by having the appointee receive the lower, unraised, salary.
"No Senator or Representative shall, during the Time for which he was elected, be appointed to any civil Office under the Authority of the United States which shall have been created, or the Emoluments whereof shall have been increased during such time..."
But Andrew Malcomb, writing for the L.A.Times has a point when he notes that the Constitution doesn't say you can evade the rule in this fashion:
It flat-out prohibits taking the civil office if the pay has been increased during the would-be appointee's elected term. Period.I'm sure Obama and the Congress will wiggle their way around this. Congress and presidents always try to ignore the Constitution when it is to their advantage to do so.