there are 5 characters in naruto that can use senjustsu(sage mode). They are in order of appearances Jiraiya, naruto, kabuto,hashirama, and minato. Now each of these characters display certain changes in appearance. Zabuza however is not a sage and never used sage mode or possessed the ability to control senjustu chakra.
All zabuza did was release chakra that shaped itself into a demon face. This caused people to call it a demonic shroud since technically it doesnt have a name. In the very pictures you provide of zabuza using "demonic shroud", he shows no physical alterations of any sort. This is all the proof you need that zabuza is not using senjustu chakra.
Also, to help you understand that zabuza is not using senjustu chakra you should re-read all chapters were senjustsu chakra is used. It gets mentioned all the time if being used. Senjustu chakra wasn't even mentioned in the match of edo zabuza vs kakashi. This is also proof that a sage mode zabuza does not exist.