iSeries user enrollment from a single iSeries works independently of any other iSeries system. Although you can enroll users on the same NDS tree, this is not recommended.
If you want to enroll iSeries users from more than one iSeries, consider having completely separate user profile sets. Otherwise, you could encounter undesirable enrollment situations.
For example, MARLA is enrolled on NetWare SERVER1 from iSeries A. MARLA is then enrolled on the same server from iSeries B with a different password than the one used on iSeries A. Now MARLA's password on iSeries A no longer matches the password on SERVER1 and she cannot start connections to SERVER1 automatically from iSeries A.