It usually can, and in most cases it should, since replacing a portal that vendors and internal teams already use creates more disruption than it is worth. The new process can sit behind or alongside the existing portal, handling the document review and assessment while the portal stays the place vendors go.
What matters is that vendor records and statuses stay in sync between the two, so nobody has to check two systems to know where a vendor stands. Agreeing early on which system owns which information, such as contact details in one and assessment results in the other, avoids most of the problems later.