Reasons for differences in Policy
Emdebian has proved to be a commercial success since the Lenny release - principally via the binary-compatible Grip distribution which has gained support from multiple companies, large and small, who are basing products (sometimes the entire future of the company) on Emdebian Grip packages.
Grip started as just a little neat idea and it is 98% automated via the emdebian-grip-server package in Debian. The problems are those final 2% of tasks which, it turns out, are nearly all based around updates to stable and dependency resolution. Grip is selective in which packages are included and we can't necessarily keep everyone happy all of the time, so some users include fallbacks to Debian for some packages. This is all supported by multistrap etc and normally works fine - until there is a lag between a Debian stable point release and the equivalent Emdebian stable release. At this stage, merely bringing in one package from unstable can mean that apt tries to bring in an update to libc6 or similar, causing chaos in the resulting dependency chain.
All users appreciate the worth of Grip being selective (no need for libreoffice to exist in the Packages files downloaded onto the embedded device), it is delays in synchronisation which cause the pain.
There will remain Policy differences between Debian and Emdebian, but as far as this integration is concerned for the binary-compatible Emdebian Grip flavour, these are limited to "the needs of embedded devices" only. i.e. manpages are not allowed in any packages, documentation must be removed and translations are handled separately.
Debian Policy doesn't describe how udebs break Policy, nor does it describe the effects of processing tools (like emgrip) but instead is concerned with packaging and best practice. Perhaps it isn't useful to complicate Debian Policy with exceptions which arise from using a processing tool on an otherwise Policy compliant package.
Discussions on -policy are primarily about modifying Policy to inform packagers - this issue is more about informing users that these particular packages in the ftp.d.o archive are slightly different to the rest and have a series of known and predictable differences from standard Policy. We can ensure that Grip packages comply with Emdebian Policy by retaining EmdebianPolicy as a diff from Debian Policy. (The diff itself is largely a list of Policy sections which do not apply or must not be applied in Emdebian packages.)
As the Grip-specific suites will have unique names, it may well be possible to utilise the same kind of support on packages.debian.org as is currently used for experimental and for udebs themselves. A note could be added along the lines of:
Note: this package is part of Emdebian Grip and does not contain translations or documentation but remains binary compatible with the Debian package at the equivalent version.