An AMD representative ("AMDMatt") has confirmed to a user's query on the OverclockersUK forum that AMD 'Raven Ridge' Accelerated Processing Units (APUs) will be getting the Radeon Software Adrenalin Edition driver releases only once in three months as opposed to the more frequent updates that Radeon GPUs get. This came across as a bit of a surprise since it was thought that the driver releases are now unified across AMD's GPU and APU offerings. The chat exchange went thus:
RavenXXX2: How come there is no raven ridge support with the last two drivers? I thought they were now unified release.
AMDMatt: APU drivers are updated every 3 months as WHQL releases only."
The 'Raven Ridge' chips had their first Radeon graphics driver update in May 2018 after their February 2018 launch while the Radeon GPUs have had multiple updates during that period that addressed stability and performance issues across many game titles. Therefore, those who have chosen to go the APU route have indeed been missing out on these goodies for a considerable amount of time despite having the same Vega core within. The AMD rep did not comment further on the matter.
Similarly, the Intel 'Kaby Lake-G' chips with onboard Radeon RX Vega graphics have also just received their Radeon Software Adrenalin driver update to version 18.6.1 on par with releases for other AMD hardware. Previously, they were running on the Radeon Crimson ReLive drivers (v17.11.2) since release.
Thus, it seems that AMD has chosen not to integrate APU fixes with its regular Radeon software updates. While moving to a quaterly release schedule is not a huge dealbreaker, it does dampen the spirits of those who bought in an APU for budget reasons and wished for a more frequent support cadence.