F5 has a great product that can be used in place of the Citrix NetScaler, the BIG-IP LTM. Although, you should watch the webcast from Citrix on how the NetScaler outperforms the F5 LTM. Citrix claims that in most test scenarios they have 3X less latency that the F5 LTM.
The deployment guide document from F5 for XenDesktop needs a little clarification for first timers. On page 7, it seems like a simple process of copying a "create-citrix-monitor.tcl" file from your local windows station to the F5 LTM via WinSCP. The TCL file can be downloaded from here. But, what you need is a "create-citrix-monitor.sh" file to run from the command line on your F5 device. The link provided in the documentation contains a script that does not work. You may receive a line error "Failed to load TMSH script". I received a replacement script from the F5 support team that can be found here. This was run on a F5 LTM with 10.2.1 Build 297.0 Final.
Take note that this script calls against a "wpnbr.dll" which exsists on the DDC, not the web front ends. Another option on the CitrixWICredentials is to create a simple send and receive string to check against web services on the web front ends.
Send string: GET / HTTP/1.1rnConnection: closernHost: CompanyVirtualName.company.comrnrn
Receive string: /Citrix/DesktopWeb
Please test this in a test environment first.