He's not splitting it with another driver, he would be splitting it with the owner and talking about just loaded miles. This is cheap!
If he were getting half of 40%, as a codriver, so 20%, on a 40/60 split, and not paying any expenses (except his own occupational insurance coverage, meals, showers, cellphone, whatever), a 1000mile run grossing $1200, would mean $240 for him, and $240 for the codriver.
At $0.25/loaded mile, he gets a bit better, at $250 for the run.
Whether the codriver is also the owner or not, should be irrelevant.
Would it be realistic to hope for 3000-4000 loaded miles/week as a team? If so, that would be $750-$1000 in his pocket per week, with only a few personal expenses.
If he got $0.30/loaded mile, he'd get $900-$1200/week.
For someone not taking a big risk as an OO, it doesn't sound that shabby to me (provided of course, he can stand living with his codriver!!!!!!!!!!!!!!!!!!!!!!!!!!) He could always decide to jump in after awhile, and buy his own truck, and get the whole shebang of revenue and expenses all to himself.