I would like to search two different SourceTypes where one SourceType pipes a dedup command on fields that only that index hasaccess to and while the other index contains all its events. Is this possible? If so how would it be performed?
Are you sure that you want "dedup"? dedup does not remove fields, it removes events that have duplicate values for the named fields. In your example, you are using a subsearch - I am pretty sure that you don't want to do that - a subsearch returns events that become selection criteria for the outer search; the events from the subsearch are not part of the results.
Please tell us what you are trying to do, as I think there may be a better way overall. Or maybe I am just confused and don't understand the question. But here is an answer to your question, sort of. To combine inputs from multiple sources, and dedup based on fields that appear in only one of the sources: