To fix this issue, please follow the instructions below.

1) Right click on Blackbaud.AppFx.ReportDB.Installer > Run as an administrator.
2) Click Edit advanced settings, then set the follow settings (see screenshot below)
Deploy OLAP cube: True
Create Report Services OLAP Data Source: True
3) After confirming that the other settings match the correct server instances and databases, click OK to save the settings, then re-deploy the BBDW.
4) After the BBDW deployment is complete, connect to Analysis Services in SSMS to confirm the UDM (OLAP) database exists. The OLAP should now show up as a data source in SSRS.

Advanced Settings for OLAP Data Source:
The Advanced Settings in Blackbaud.AppFx.ReportDB.Installer