Hi Martin,
do you have a cross compiler installed on your BBB? Which board/mcu are you targeting?
I don't think that there are binary packages of the
https://launchpad.net/gcc-arm-embedded toolchain for running on ARMv7.
Regarding the ocaml packages, what distro/version are you using and how did you install the packages?
Also you don't really need ocaml-native-compilers, this package just provides the compiler in a native implementation which results in faster builds, but the "normal" bytecode compiler works just fine.
Can you post the errors you get?
Cheers, Felix