Well, I assume it is correct as the rom compiles, is flashable and boot.
I have the feeling that recovery is broken in Omnirom.
Yesterday I build CM11 (nightly sources) for Galaxy Tab 2 (gt-p5100) and I get the same "No private recovery resources for TARGET_DEVICE p5100" message. BUT the rom is working AND the recovery too !
The fact that the recovery from Omnirom is not booting as therefore nothing to do with this message.
I'll keep on searching and, more important, learn
One month ago I didn't know anything about building a rom but I had some knowledge about compiling the Linux kernel.
Anyway thank you for your help.