Spira and KronoDesk let you import existing users from LDAP into the system. That will bring over the users, and also link their user profile to their LDAP user by means of the LDAP Distinguished Name (or DN). However if you move a user in the LDAP folder structure, it may break the link with Spira, resulting in that user not being able to login.
Integrating SpiraTest, SpiraPlan or SpiraTeam with your LDAP or ActiveDirectory direcory server makes a lot of sense. It allows you to have a single user authentication system, with all logins and passwords centrally managed. Spira includes integration out of the box with LDAP and this article provides help for some common issues that we have come across.