bpel is a type of component in the SCA container, which is SwitchYard. bpel components are run with riftsaw engine, but the interactions between components, in the SCA composite are handled by SwitchYard.
All these components can be exposed for consumption (services) or can call another services (references). These services/references need to have an interface that define their contract, whether is java or wsdl, and will interact to the outside world via a binding, that defines the communications channel/protocol.
a Bpel service will invoke another components (partnerlinks) usually defined with a wsdl contract, and these components can be defined in the same composite application, or in other application, in which case, communications between these two composites can be using SCA bindings. So yes, answer is BPEL can call/use/invoke services/components exposed via an SCA binding.
not only our product does it, as you mention, most SCA implementations that have bpel components will be able to communicate via their SCA binding. But this binding is implementation specific, so SwitchYard can only use Switchyard's SCA components.
I hope I have helped you to clarify your understandings.
Is there an example of BPEL calling SCA component in SwitchYard? In the downloaded package, or somewhere else.
Have a look at the bpel-loan-approval quickstart. The loanService invokes the riskAssessor service through a reference. The invoke/service in the deploy.xml identifies the SwitchYard service that will be invoked for the specified partner link. Notice that the QNames for the services in the deploy.xml match the QNames for the services in the switchyard.xml file.
Hope that helps.