It figured out what I was doing wrong.
First extract the base exe installer...
"AcroRdr20151500630033_MUI.exe -sfx_o"D:\AdobeRdr2015" -sfx_ne"
Then run msiexec /a to create an AIP. Be sure to specify a new folder as the destination
"msiexec /a AcroRead.msi"
Finally patch in the AIP in the new folder with the MSP file.
"msiexec /a d:\Acroread2015AIP\AcroRead.msi /p AcroRdr2015Upd1500630244_MUI.msp"
Deploy from the msi in the AIP folder.