It is said that MSTP is used to group VLANs for different logical topologies. Can it be used to group individual VLANs (one VLAN per group) to imitate the behavior of Cisco's Rapid PVST (unique logical topology per VLAN)?
Yes it can. In this case, you'll need to create an MSTP instance (in all the switches invloved) and include only one VLAN in that instance.
Sample configuration on a cisco Catalyst switch:
spanning-tree mode mst spanning-tree mst configuration name NAME revision 2 instance 1 vlan 10
Note: This will work as long as the number of VLAN's for which you are creating separate topologies is less than or equal to the maximum number of MSTP instances you can creat on a switch. This maximum is in turn determined by the switch model, software version and/or license level.