[multistrap] has had support for selecting packages from particular components of a Debian repository since 2.0.5 (Squeeze has 2.1.7, so every available version has this support).
When mixing Emdebian and Debian, it can be important to understand the Emdebian Grip Components which separate out the development packages, the documentation packages, java packages, and debug packages into separate components.
In Debian, components are used for legal reasons, to separate main from contrib and non-free.
In Emdebian, components are used to reduce the size of the Packages files which need to be downloaded onto the final device.
Most installations of Emdebian are not typically used to build packages, so all of the tools which are used to build packages in Debian are sorted into the dev component of Emdebian Grip.
If your multistrap configuration tries to mix Emdebian and Debian and then include development packages then you will need to use the component support of multistrap to make the Emdebian Grip dev component accessible as well as the default main
Add a components (note the plural) field to the Emdebian section of your multistrap configuration:
[Emdebian] packages= source=http://www.emdebian.org/grip keyring=emdebian-archive-keyring suite=squeeze components=main dev
Note that you must include main if you are overriding the default components field.
This prevents failure messages like:
The following packages have unmet dependencies: libc6-dev : Depends: libc6 (= 2.11.2-10) but 2.11.2-10em1 is to be installed