Dimensional model or Relational model for data warehouse?
The point of a data mart / warehouse is to facilitate analysis for non-DBAs. The relational model is wonderful for transactional databases to speed writes integrally, but is harder to understand for non-DBAs. 

A data warehouse is a collection of data marts, or can act as a central data mart. If you are going to use dimensional modelling in your data marts (as you should), then you should use it in your warehouse as well.

You will find that most companies use regular RDBMSs (say, Oracle, SQL Server, Postgres) for their data warehouse, though you probably want one that supports materialized views and easy table partitioning. Some companies use columnar databases (say, MonetDB) or NoSQL databases (say, HBase) as well.