If I dual connect my access switch to my 6509s running vss, what will happen, will spanning tree still block one of the ports if I don't set up an etherchannel?
Assuming a basic topology where there is no VLAN trunking etc going on then yes, STP will block one of the links as you have created a layer 2 loop.
If the links were VLAN trunks and carrying all VLAN's on both links, the above blocking scenario would also apply.
If the links were VLAN trunks and only carrying a subset of VLANs on link #1 and another subet on link #2 (e.g. VLAN's 100 and 110 on link 1 and VLAN's 200 and 210 on link 2) then no blocking would occur as there would be no layer 2 loop.
That should cover off pretty much all the scenarios you could use