Hello Thisisnotaswan,
In brief the answer is yes you can share 5GHz band for backhaul and client traffic.
From the user guide :
A mesh radio’s bandwidth can be shared between mesh-backhaul traffic and client traffic. You can, however,configure a radio for mesh services only.
If you configure a singleradio AP to deliver mesh services only (by disabling the mesh radio in its 802.11a or 802.11g radio profile) that mesh node can not deliver WLAN services to its clients.
DSP