I have a network topology as shown in document in the attachment. If second provider doesn't tunnel BPDU packets(i.e. missconfiguration), is it possible to have a layer 2 loop? Will PROVIDER 2 drop bpdu packets, or there is some mechanism that will take care situations like this?
yes your switches need to be aware that both links are going to the same place unless you are permitting two different sets of vlans with no overlapping it will create a loop.
providers switches cannot distinguish between vlans to be tunneled and vlans to be blocked you need to use
swithcport trunk allowed vlan
to define only the needed vlans that should go over each pipe.
Hope to help