Mostly yes, from https://wiki.ubuntu.com/Ubuntu/ForDebianDevelopers
Most source packages in all Ubuntu components (about 4 in 5 at the
time of this writing) are copied unmodified from Debian, but other
sources include apt-get.org, REVU, directly from organisations such as
Blackdown and WineHQ, software which has been packaged by Ubuntu
developers, and packages created specifically for Ubuntu.
In some cases, the same upstream software is packaged separately in
Ubuntu and in Debian, though this is to be avoided unless there is a
justifiable reason to do so.
Where packages in Debian and Ubuntu have a common heritage, the
packages use version numbers which reflect this.
This only refers to source packages - all binary packages are built on launchpad using the current toolchain in Ubuntu