Q. How similar is the ipk format, to the deb format? They look very similar; the data and control tar balls are identical as far as i can tell.
A. Very similar. ipk files are basically deb files with documentation removed, and ipkg is even supposedly able to handle deb files. Opkg can install .deb packages directly, with no change.
If package contains binary data, you can repack it only compiling the source code.
What exactly do you want to achieve?
If you need OpenSSL, it's here: https://openwrt.org/packages/pkgdata/openssl-util
I have proprietary packages OpenVPN and OpenSSL for debian (not source code) under the arm and amd64/i386 platform.
I need to install them under mips platform (rb2011uias-2hnd)
While it's possible to build OpenWrt with glibc/ libstdc++, any non-trivial package depends on a myriad on other libraries as well, each with their own ABI incompatibilities relative to packages build against Debian or other desktop distributions.
If you plan to virtualize anyway may I suggest to run two virtual machines, one running OpenWrt and one running Debian, and just network them together.
This is not a strict requirement - I now have only a mips router. Package maker compiled them only under i386 and amr. I want to experiment - compile openvrt with the support of necessary libraries C and install packages for i386