In our recent project we were using Dynamics 365 for Sales Connector of Informatica Cloud to push data into CRM from SQL DB.
To update the lookup instead of using GUID we decided to us the Alternate Key.
From the below KB article, it looks like the older version of the informatica connector wasn’t supporting the Alternate Key
However, the newer and the recent version of the connector based which is based on Web API supports the alternate key.
To set the alternate key we basically need to use the below syntax,
Hope it helps..