Not so. There is overlap in what SAS and various database products can do, but neither is completely subsumed by the other. And, even in the areas that they overlap, one might do the job better/easier/faster than the other.
Also, you will want to define what you mean by "database" (or data base). The SAS database architecture is not truly relational, so a suitable DBMS or RDBMS replacement with SAS would ned to be determined on an individual basis.
What you mean when you say that the SAS database architecture is not truly relational? You can create fifth normal form databases with indexes and constraints in SAS, and you can create completely denormalized databases in Oracle. So what is the essential difference?
I wouldn't say that SAS is always relational, but it can be relational, just as Oracle can be relational (or not).
Saying that a relational database can't be implemented in SAS (especially if you have some of the newer SAS products like TSPL) would be overreaching. Saying that all Oracle or DB2 or (fill in commonly used commercial database name here) databases are relational would be just as much of a stretch.
In other words, it's the design that makes something relational, not (just) the platform.
I agree with Jack on the relational part. Relational models can be implemented un SAS. Database functionality to support the integrity of relational models exist in Base SAS, not in SPDE/SPDS.
What I think is not fully implemented in SAS is MS part of RDBMS, which means integrated user management, storage management, logging, change tracking etc. So I think when building mission critical systems, one tend to look for other storage solutions than SAS.