Hi Leo,
1) Do I must to have 10GbE interface to implement it?
Yes, the VSL links between the 2 switches need to be 10Gig links
2) I have some servers connected only to one of my 6506-E. Should them be connected to both of my 6506-E if I implement VSS?
If your servers have 2 NICs, yes, you should connect one link to each 6506-E using Portchannel. This way you have switch and NIC redundancy.
HTH
Reza