Is possible to add a non-aggregated measure to an OLAP cube? for example I have a 'Datetime' field in my relational DB, and I would like to not use any kind of aggregation function when querying this measure of the cube. is there any scenario where this could be possible?
Generally you'll only have aggregate data in an OLAP cube, since the main purpose of the cube is to pre-aggregate the data.
While you could add the datestamp as a Dimension, and have each value in the cube representing a single record in your relational database, you'll lose much of the performance benefit of having the data in an olap structure.
A better way, if you need to drill-down to the level of individual transactions is to have your application transition to using the relational database for these queries.