What a mess.

First, is BMWNA claiming there is no warranty BECAUSE the dealer didnt change the oil??? If yes, and this is in writing (I can virtually guarantee you this is all phone calls and messages, right?) then get a lawyer involved.

If they are now separate issues, you need to know what is causing the CEL fault.

Did the dealer tell you what part is bad and is causing the DMTL issue? Find out what 'vacuum pump' is covered by BMWNA in the CA warranty. Do this WITHOUT tipping your hand.

Generally people spill their guts and tell their 'story' to the nice agents on the phone- and these people are experts in screwing you. They make it sound like they are dedicated to getting to the bottom of your issue- but in fact they are trying to (1) protect BMWNA, and (2) protect the dealer, if possible. Essentially BMW is saying 'you are on your own with the dealer, feel free to sue them- but we arent doing a thing'.

If your lawyer can force BMWNA and/or the dealer to go on the record with the 'failure to change oil' issue, this may be leverage. At the very least getting this on record may help you later. Did the dealer file a maintenance claim with BMWNA for work never done?

Anyway, first step is to diagnose your emissions fault. Find out if it is a warranted part.
Then demand to BMWNA in writing. Force them to refuse in writing.
Then escalate, letters to CA CARB. Complaint.
Then go after the dealer for defrauding you and voiding your warranty with BMWNA

my 2 cents