DBCC on SSAS Cube fails
Did you read the rest of the docs?


  Output when running DBCC against an earlier version of Analysis
  Services
  
  DBCC is only supported on databases running on a SQL Server 2017
  instance. Running the command on older systems will return this error.


Executing the query ...  
The DBCC element at line 7, column 87 (namespace http://schemas.microsoft.com/analysisservices/2003/engine) cannot appear under Envelope/Body/Execute/Command.  
Execution complete


Updated
Here is a link that explains things a bit more in detail than the docs you're are referencing.

https://www.mssqltips.com/sqlservertip/4077/consistency-checks-for-sql-server-analysis-services/