American Express Membership Rewards - using airline miles to upgrade on pay with MR points ticket

I haven't seen this posted anywhere and am wondering:

If I use the MR pay with points feature to buy a Delta (or UA, AA, etc) ticket will Delta allow me to use Skymiles to upgrade to a higher class of service?

I can't see why not, since in essence you purchase the ticket and then get reimbursed by AMEX.

Any recent experiences with this?

Thanks!

it should work, MR points basically just refund you $XXX of your total ticket purchase, so should be no restrictions on upgrading via FF miles

As far as I know (no firsthand experience), the airlines don't even know that you purchased the tickets with membership rewards points.

Just make sure you buy an upgradeable fare class and better yet also see if there are upgradeable seats available via something like expert flyer.