There is no more need to install Raspbian first.

all Devuan ARM images are now directly installable just like raspian
is. not just the Rpi2/3 image, but all others, will work the same: dd
on a SD card and boot.

and yes, in case you are asking yourself, not even Debian does provide
that ATM. We already include actual embedded platforms as installer
targets, which is handy and consistend with having a unique base.

ciao