In short, yes, the first created user (the only one created by D-I) is added to the "audio" group, among a few others.
with systemd as the default init system. systemd/ logind sets the right permissions for the sound devices [1], so I think it is unnecessary to add somebody to the audio group. (And missing all the "fancy stuff" systemd brings to us.) Thanks, floris [1] $ getfacl /dev/snd/* ... # file: controlC3 # owner: root # group: audio user::rw- user:floris:rw- group::rw- mask::rw- other::--- # file: pcmC3D0p # owner: root # group: audio user::rw- user:floris:rw- group::rw- mask::rw- other::--- # file: seq # owner: root # group: audio user::rw- user:floris:rw- group::rw- mask::rw- other::--- # file: timer # owner: root # group: audio user::rw- user:floris:rw- group::rw- mask::rw- other::--- ...