FortiSwitch QoS DSCP markings

I have a requirement for QoS for voice traffic and was wondering what exactly I need to do to make sure it is tagged correctly.  The VOIP vendor is requiring DSCP 46 tags on the the Voice VLAN (which is also 46).  The traffic will only go through their ADTRAN and not the Fortigate we have so I don't have to worry about the traffic through the Fortigate.  The ADTRAN will be the default gateway for the phones.

Question 1.  Can I do this at the VLAN level?

Question 2.  Do I have to set up all the CoS queues etc?

Question 3.  Is there a way to just trust the DSCP markings from their router?