Depends on what you mean by "use MPLS QoS", but most likely answer is - yes.
If packet is MPLS switched over WMM enabled link - either by "normal" hop or penultimate hop, WMM access category will be chosen based on EXP bits of received label (because EXP gets copied to "priority" field). In case packet arrives to router using MPLS switching and is further routed over WMM enabled link (router is egress for LSP), care must be taken so that correct "priority" is assigned to packet:
- LSP egress router must receive packet with label (this implies that explicit null label should be used by penultimate hop) - this will cause packet "ingress priority" to be set to value carried in EXP.
- correct firewall rule that sets "priority" from "ingress priority" must be configured.