Update
After creating an SCCM deployment specifically for Acrobat DC, it appears that in combination with the Creative Cloud desktop client, updates are completing as expected. IIS log demonstrating this below:
HEAD /Acrobat/arm-manifests/win/ArmManifest2.msi - 80 - #.#.#.# Microsoft+BITS/7.8 - 200 0 0 31
GET /Acrobat/arm-manifests/win/ArmManifest2.msi - 80 - #.#.#.# Microsoft+BITS/7.8 - 200 0 0 0
HEAD /Acrobat/pub/adobe/acrobat/win/AcrobatDC/1901020069/AcrobatDCUpd1901020069_incr.msp - 80 - #.#.#.# Microsoft+BITS/7.8 - 200 0 0 15
GET /Acrobat/pub/adobe/acrobat/win/AcrobatDC/1901020069/AcrobatDCUpd1901020069_incr.msp - 80 - #.#.#.# Microsoft+BITS/7.8 - 200 0 0 609
It's not ideal, but until Adobe can introduce the base installation for Acrobat DC like all other products - this at the very least, works without needing to grant special access to our users through our corporate proxy. The updates are also automatic - so other clients obtained the incremental update without an issue.
At this point in time, there is no correct answer, and the issue remains unresolved from the originally stated issue.