if I am using LDAP as authentication backend, is it still possible to use NTLM between browser and Web Gateway so that my users are not prompted for their credentials (NTLM will push the Windows credentials)?
No. This is not possible because of the cryptography in play with NTLM.
You must use NTLM, NTLM Agent or Kerberos on the back end to utilize the Integrated Authentication with a browser.
Retrieving data ...