Maybe so with earlier Netware.. I am not certain (currently running 6.5). I have worked a fair bit with support on this issue and they assure me it will not work on Port 389 (and indeed it doesn't even if I disable SSL on the server). I was using port 389 when I initially tested the software and it stopped working on the newer firmware.
According to support the software will not work unless you use SSL on port 636 and in my testing I have found this to be true. (I haven't tried SSL on another port but its turned off until the other bugs are worked out). Educated guess says that SSL would work on another port if you changed the LDAP object and the webadmin to use the same port. 636 is just the default SSL port for both and SSL is required.
The point is if it does not work unencrypted on port 389, then it should not be an option let alone the default option. It's a minor thing but will save Astaro some support time if it is corrected.
We have a running setup using port 389 and no SSL and I know several customer installations, that run it like that. So while your information may be correct in some cases (which I haven't heard of), it is wrong in general.