dual boot Mountain Lion/Mountain Lion I got a Macbook Pro with OS 10.8 installed on, the usual recovery partition that is created by the OS installer, and a 35GB partition (currently NTFS, but I can reformat in HFS+ if needed).

My question is : can I use the recovery partition to do a full OS 10.8 installation on the small partition, in parallel with my everyday-use installation (i.e. will it let me do that without erasing/wreaking havoc on my current OS, is there any known caveats, and so on)?
You WILL need to reformat the smaller partition from NTFS to HFS+ before booting to the installer but otherwise it's pretty straight forward.  When you boot to the installer / recovery partition you will eventually be prompted to select the installation destination, choosing the smaller partition will tell the installer to install 10.8 on that partition rather than your main partition.

Once the installation is complete you can choose which one to boot into either by specifying it in System Preferences > Startup Disk or by holding option at startup and selecting the proper partition.