He will probably make less, a quick google search shows practice squad players make a max of $216,000 vs his salary at Gloucester which was reported to be approximately £225,000. He could've almost certainly earned more than that in rugby if he'd gone and played in France or Japan.
However the practice squad salary is certainly worth the gamble, should he get signed to one. As the most high profile athlete to go through that international programme, I'll be surprised if he isn't.