This is, as with everything, VA site specific, but I imagine quite rare in general. Typically the VA would negotiate with the residency for expectations like night coverage of an ED or being on call. It would be part of the overall contract with the residency and thus an expectation as part of your general training, not something for extra pay. The amount of ongoing paperwork at the VA to maintain individual credentialing for a panel of moonlighters would be untenable in most cases and no, your residency credentialing would be harmful rather than helpful as that is a whole separate thing for trainees. Every VA has a department dedicated solely to trainee credentialing with at least 3 clerical staff for a small facility, it's that ongoing much work.