The receiving Splunk doesn't know what is being sent, it only processes events it receives over the port configured as an input for the receiver. I am not exactly sure what you are trying to determine, but depending on the type of forwarder you are using, sourcetypes may not be possible to configure. On both the universal and lightweight forwarder, you cannot set sourcetype. This is done where the data is parsed, on the receiver. The search summary page should give you a pretty good indication about the number of sourcetypes that have been seen on the indexer.