Will an old DUI haunt me for the E7 promotion board (SSG Evaluation board)?

Short answer: Yes. However, I assume you're looking for the longer answer which is "how much will it haunt me and will it stop me from being promoted"? Anything you get will be a subjective answer.

The instructions to the FY23 SFC board members* were to look hard for examples of five threshold behaviors - Integrity, Empathy, Discipline, Physical Fitness, and Mental Agility - in the Soldier's career, both where they have demonstrated them or where they failed to demonstrate them. A board member coming across your file might absolutely consider this a failure on your part with regards to Discipline*. However, others might not. Again, subjective.

I told someone that asked a similar question once that one person will look at your DUI when you were a junior NCO (I assume based on timeframe and the -R eval) as a momentary lapse in judgement while another will look at it as you were phenomenally lucky that you didn't crash into a pregnant lady that was driving a van full of nuns.

From your description, you've done work to put marks in the positive column in order to overcome the big one that was placed in the negative column. What else can you do? In the AAR*, the board said they gave the most weight to someone's NCOERS. At this point I would expect that is out of your control except for possibly your next one.

One comment that you CAN do is pay attention to your Soldier's Record Brief (SRB) and Official Military Personnel File (OMPF). The board noted that a high number of outdated SRBs and OMPFs that were missing documents. Make sure your most updated civilian transcripts are included and absolutely make sure you certify "My Board File" on iPERMS after you review it (less than 50% were certified).

Aside from that, there's not much you can do at this point. What will happen will happen. Would it behoove you to have a plan B? Yes, I would explore options 'just in case', but don't commit yourself to a COA unless you are planning on a path regardless of the outcome of the board.
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* MOI to Board Members - https://www.hrc.army.mil/asset/26657
* Discipline as defined in the MOI - NCOs must control their own behavior in accordance with Army Values, and obey and enforce orderly practices in administrative, organizational, training, and operational duties. NCOs uphold good order and discipline, enforcing Army standards for themselves and those around them.
* AAR - https://www.hrc.army.mil/asset/26653