I disagree strongly.
Willard indirectly endorsed Trump's “birtherism” when he embraced not only Trump's endorsement but in promoting Trump as a surrogate, i.e. a man whose opinion he values and whom he is asking others to respect.
Willard's strategy is tactically brilliant and cynical, which is to distance himself personally from Trump's “birtherism” while endorsing Trump as a wise and valued counsel.
Willard is only saying his campaign is not going to directly pursue Barry's ineligibility, but Willard has not denounced Trump's past and recent statements on the merits.
This is driving Barry, Axelrod and Jarrett crazy as all of their surrogates are falling all over themselves to try to get Willard to denounce Trump's statement, but he hasn't, yet!
Bingo! Romney may be the first GOP candidate in a while who has figured out how to use surrogates.
There's no gain for Romney to take a position in the "birther" controversy. Nobody has yet developed any proof that Obama might be in eligible. All is speculation, so the default position is that he is eligible.
Let Trump pursue that line of attack. See if he can generate some proof. If he can, well and good. If he can't, no harm done.
In any event, Romney is going to have to beat Obama at the polls -- not in the courts.