I agree that VA disability may not be a classified as a pension but I believe that the DTA would still exempt it because of these two articles. The primary consideration IMO is that it is from government service.
Not everything has to be specifically mentioned. The phrases "...other similar remuneration..." and "Remuneration, other than a pension,..." can cover a lot.
ARTICLE 20 Pensions and Social Security Payments
1. Subject to the provisions of paragraph 2 of Article 21 (Government Service), pensions and other similar remuneration paid to a resident of a Contracting State in consideration of past employment shall be taxable only in that State.
ARTICLE 21 Government Service
1. a) Remuneration, other than a pension, paid by a Contracting State or a political subdivision or a local authority thereof to an individual in respect of services rendered to that State or subdivision or authority shall be taxable only in that State.
BTW my military retirement pay for 20 years active duty service is not called a pension either.