It would be wasteful to use this approach for non-sparse matrices, but it would still "work".
In other words, numpy is damn-fine with matrices, but if you can replace DBMS->network->ORM->numpy->ORM->network->DBMS with just some SQL, it's pretty clear which will be faster.
On the other hand, if your data isn't already in an RDBMS in matrix-like tables, there is little point in moving it to one just so you can use tricks like the one mentioned in this article.