I recently got off the phone with the Marriott loyalty department and wanted to share the discussion.
According to the representative, after combining your accounts, your SPG lifetime nights will count towards the legacy lifetime status criteria. However, the points will not count (although they will be converted for your rewards redemption.)
So for example, I had 440 nights with Marriott, and 47 nights with SPG. After combining, I now have 487, and will only need 13 nights to be grandfathered into the Lifetime Gold under the old program (Lifetime Plat in the new program), points requirement aside. The rep confirmed this scenario to be valid.
Given the conflicting information we've received from the different representatives, is anyone else able to confirm or have they heard otherwise? Thanks!