As of 2018 the Managing Indexers and Clusters of Indexers : Additional roles for the master node now definitively says No
Additional roles for the master node
As a general rule, you should dedicate the Splunk Enterprise instance running the master node to that single purpose. Under limited circumstances, however, the master instance can also fulfill certain other lightweight functions . . .
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!!! Caution: Do not colocate a deployment server on the master under any circumstances.
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