A little more technical detail for your information...
When you do LDAP authentication on an Aruba controller, the controller attempts to bind to the LDAP server using the user's credentials. If the bind is successful, we interpret that as a correct set of credentials, and the user is authenticated. This also generally means that the controller needs to get the user's password in plaintext, so that it can carry out the LDAP bind. With captive portal, that's easy. With 802.1X, that's not easy. Most 802.1X supplicants are set up with PEAP-MSCHAPv2 by default. Using this method, the controller never receives the plaintext password - only the MSCHAPv2 hash of the password. WIthout the password, the controller can't bind to LDAP.
There are other ways of dealing with MSCHAPv2 hashes. If the LDAP server stores the password as an MSCHAPv2 hash, then in theory we can bind to the database as an admin user, pull down the user's hashed password, and do a comparison. I've never seen this work in practice outside of a lab though, and it is highly dependent on how the LDAP server stores data internally.
To get around this issue and still let LDAP work, Aruba produced a PEAP-GTC plug-in for the Microsoft 802.1X supplicant. It still uses PEAP, but adds a different inner method which uses GTC (Generic Token Card). GTC was designed for SecurID tokens and other one-time passwords, where sending the cleartext password isn't considered a security risk. When used for username/password authentication, it does allow the controller to receive the cleartext password, and thus lets you work with LDAP successfully. But it means rolling out client software, and that's the administrative overhead that others have commented on in this thread.
To cut to the chase, 802.1X was designed with RADIUS in mind. PEAP-MSCHAPv2 fits into the natural order of how RADIUS operates. Where LDAP is designed as a database, RADIUS naturally handles challenge/response protocols like MSCHAPv2. So I'll offer the same advice that others have - use RADIUS and Be Happy.