Yes, most pension application papers I see have a space for Comrades to validate the soldiers service.

In this application, I see three witnessess who I assume were attesting to his service, I believe I read them as:

R. D. Cochran, John Dermak, H.P. Nalloy

None of these men appear on the roster of the 37th. However, as the application is dated 1924, these fellows may just have been able to state he enlisted and went off to war.

Again, Mills enlisted in 1865, and as there are no company muster rolls available for 1865, there is no way to attest to his service
outside of an approved pension.