You actually can. What you need, to have from both switches access ports (so they VLAN is irrelevant, as there is no tag on packets), than configure 2 ports on AP in different VLANs (also as access ports) and you can create 2 different SSID, terminated to this 2 VLANs. What you can't do, put both of them on 1 SSID, as for AP this are diffrent VLANs.
VLAN is a local thing and makes sense in a switch only, when packet leaves a switch, tag may change or be removed at all.