Time to vote on the openSUSE Strategy!

"Could you please point me to the equivalents of Open Build Service and openSUSE Studio in Gentoo?"

OBS is a fine thing and Gentoo doesn't need to duplicate that. A backend will serve the purpose however there is no such thing as "openSUSE Studio". There is SUSE Studio which is a proprietary product from Novell. I don't think anyone in the openSUSE community has a reason to be proud of it.