Question:
What is the vmware recommendation for ESXi...to boot from SAN or local disk?
Answer:
Both are supported, and Preferred would be Local storage.
Below are the location of some documents for more details:
https://blogs.vmware.com/vsphere/2011/02/ops-changes-part-3-local-disk-vs-usb-vs-bfs.html
http://pubs.vmware.com/vsphere-55/index.jsp?topic=%2Fcom.vmware.vsphere.storage.doc%2FGUID-C1FD30A2-27C1-45A6-A736-E0AE76A0ADB2.html
http://pubs.vmware.com/vsphere-55/index.jsp?topic=%2Fcom.vmware.vsphere.storage.doc%2FGUID-2A66A330-A9E5-460B-8982-54A1B1C38C02.html
http://pubs.vmware.com/vsphere-55/index.jsp?topic=%2Fcom.vmware.vsphere.storage.doc%2FGUID-9004389B-E2C0-4BE5-811C-E4886E3B7450.html
http://pubs.vmware.com/vsphere-55/index.jsp?topic=%2Fcom.vmware.vsphere.storage.doc%2FGUID-9004389B-E2C0-4BE5-811C-E4886E3B7450.html