The guidelines in Section 508 are there to make the Us Federal Government accessible to all US citizens, not to create "Section 508 compliant" technology. The distinction is very subtle.
All US citizens have a right, under the Americans with Disabilities Act, to be able to access certain federal government information. So, say, for example, the government will require all US citizens to submit our tax forms online and in a certain format. The government will use Section 508 to evaluate document types and submission portals to determine the most accessible doc type and portal. Those doc types and portals that are not accessible cannot be used UNLESS the government has no other accessible doc type and portal AND they allow for alternative submission, e.g., via mail or email in a different doc type.
The requirement to "comply" is on the government, not the vendor. However, the government will choose technology based on accessibility using Section 508.
And, none of this applies to the Department of Defense.