I think the reason for the problem is a combination of drawing the sky to the gbuffer's color RT (which is a R8G8B8A8_UNORM_SRGB surface)

Usually the GBuffer stores surface albedo, which is a 0-1 fractional/percentage value. A skydome is more like an emissive surface though, than a regular diffuse surface, so yeah, it doesn't make sense to render it into your GBuffer's albedo channels. When adding emissive surfaces to a deferred renderer, the usual approach is to render these surfaces directly into your light-accumulation buffer, instead of into the GBuffer.

Regarding SRGB and LogLUV: when using an SRGB texture, it will go through a linear->gamma transform when writing, and a gamma->linear transform when sampling, so it shouldn't have much of an impact, but it can mean that the value that you sample later is slightly different to the value that you wrote originally. This transform is only designed to be used to store RGB "colour" information in a perceptually efficient way (distributing more bits to darker colours) where it doesn't matter if there is a slight change in the values.
However, LogLUV splits the L component over 2 8-bit channels, and if either of those channels is slightly modified, then when you reconstruct the original 16-bit value, it will be wildly different. This makes it more of a "data" texture than a "colour" texture, and so SRGB encoding should not be used.

I think the reason for the problem is a combination of drawing the sky to the gbuffer's color RT (which is a R8G8B8A8_UNORM_SRGB surface)

Usually the GBuffer stores surface albedo, which is a 0-1 fractional/percentage value. A skydome is more like an emissive surface though, than a regular diffuse surface, so yeah, it doesn't make sense to render it into your GBuffer's albedo channels. When adding emissive surfaces to a deferred renderer, the usual approach is to render these surfaces directly into your light-accumulation buffer, instead of into the GBuffer.