Am I still allowed to wear my dress uniform/blues?

I recommend you do not. And here is why. No one would know that you ETSd and you would not be seen as a retiree. Therefore, pretty much everyone in uniform there would consider you as still serving and would expect you to follow all the customs and courtesies required/expected. Just imagine the possible reaction of the first Officer or NCO there at the graduation towards you if (when) you don't salute or stand at Parade Rest. It's just unneeded headaches. Plus, that day belongs to your wife. Wear your best civilian attire.

Wearing a dress uniform as a civilian is for retirees. It would be inappropriate for you to don your old uniform unless you were in the Reserves

This is your wife's graduation, not yours. Just wear something nice and let her have her moment. You don't have to try to upstage her...

Short answer: No. Better answer: let her be the center of attention on her graduation day.
A lapel pin on your suit jacket signifying you are a veteran would be a better choice.

My Dad was an LTC in the Marine Reserves when I graduated from Army basic. He showed up to graduation in his civilian clothes. I asked him why he didn't wear his uniform. He told me that if a Marine LTC showed up in uniform unexpectedly, it would make a lot of trouble for everyone. They would probably feel obliged to make a fuss over him, especially since he was from another service, and invite him up on the dais with the Bn and brigade commander. He said this day is about you, the other graduates, and the people who trained you. It's not about me.
In any case, you're not in the military anymore, so it wouldn't be right to show up in your uniform, because as others have said, they would assume that you are. They probably wouldn't put you on parking lot detail, but it would be awkward, especially when you went to meet her Drill Sergeants.

I have my dress Uniform hanging proudly in my closest for over a decade now. From time to time I look at it, reminisce about the units I was in and how I had worked hard for my ribbons and devices.
I even have put it on now and again (noting that some places need let out a bit well maybe more than a bit lol) but I have never worn it again in public since I got my DD214. I have been asked on a couple of occasions why I don't wear it for certain social events and my answer is always the same. "I may always be a soldier, but I am not an active soldier, that uniform is reserved for the honor of those still serving." You can still show your pride by wearing a lapel pin that has your favorite unit, or posting, a US Army Veteran, or something like that, but don't be THAT GUY that wants to wear his dress uniform to "show off". This is your wife's day of honor, support her, be proud of her and honor her with her accomplishments by being the best dress Husband in a suit. You wanna show off your Greens, put it in a shadow box and hang em on the wall, do a ribbon case with your issued flag, whatever the case treat your service and greens with respect and dignity. You did earn that uniform, but adopt my line of thought and you will do well. "My beret and my Uniform are just like me respected but retired."

If you were going to a Funeral for a discharged or retired friend or family member YES, or a Military Wedding, I was an active Duty SPC and went to my Sons Graduation at Ft. Jackson and wore Civilian Clothes