It isn't necessary to match apps and dlls but it's a Good Thing To Do.
If it will never happen a situation where one side allocate memory and
the other free it, and if none of the sides relies on memory appart
from what it gets via function arguments then there shouldn't be any
problems (if I'm wrong somebody please correct me).

To put it simply if your dll does malloc/new then it must free/delete.

If it is really necessary to pass buffer management to the other side
then there should be a function from buffer creator's side available
to buffer receiver for buffer deallocation.

In another words if there is a function in your dll:

char* CreateNewBuffer(void);

ther there should be as well:

void DeleteBufferCreatedInThisDll(char*);