Yes.
Although Open Source Portfolio runs in and depends on the base Sakai Sakai describes itself as a "Collaboration and Learning Environment" (CLE). A CLE is an environment where professors can prepare and deliver courses, communicate, and collaborate with their students, It can also support ad hoc group collaboration, electronic portfolios, and research collaboration. In education, the most common term to describe the teaching and learning part of this tool set is "Learning Management System" (LMS).">Collaboration and Learning Environment, you can enable and use OSP tools without turning on or using any Sakai collaboration or course tools.
Alternatively, you can enable and use only those Sakai tools that may be useful in your specific portfolio environment, for example, Sakai's announcements, mailling list/archive or calendaring tools.