Yes, due to XenServer's usage of industry-standard open source Linux device drivers, the actual hardware compatibility for XenServer is broader than what is listed on the HCL. Additional configurations that are reported to work with Citrix XenServer are listed at the Citrix Ready Community Verified web site. Users are encouraged to submit their own configurations to the Community Verified site, to guide other users as to the configurations they might wish to use.
For servers and storage not specifically listed on the HCL, Citrix provides a self-certification test kit and program which includes the necessary tools and instructions for validating hardware against XenServer. This can be used by hardware vendors to certify their own hardware in order to be listed on this HCL. It may also be possible to submit hardware certifications on behalf of a vendor, however agreement from the vendor will need to be acquired before embarking on the certification process. If you are unsure, then please get in touch with the HCL team first.
Completed self-certification test results can be submitted by signing up at XenServer Tracker website and creating an issue in the project "XenServer Hardware Compatibility List (HCL)" with issue type set to "HCL Submission". Once the submission has been reviewed and accepted by the XenServer HCL team, the hardware can be added to the HCL and will be eligible for full support.
If you have any XenServer HCL-related questions or comments, please use create an issue in the same project using the Issue Type "Enquiry".
Unless specifically mentioned, if a piece of hardware is supported for a base product release (e.g. XenServer 6.5) it will be fully supported by Citrix with any applied service packs or hotfixes (e.g XenServer 6.5 SP1).
You can find these on the Citrix Ready Marketplace.
You can download the hardware certification kits for XenSever 7.0 from here.