Yes, that's actually the more common way of expressing it.
While 'hvis' is a lot more elegant, it's falling out of use to such a degree that we may remove it in a later tree version. Some, particularly of the younger generation, will use 'hvems' instead, but that's incorrect in writing and sounds uneducated in most spoken dialects.
'Hvem sin/si/sitt' is perfectly fine in any situation, and also present in the course. :)
Choosing sin, si or sitt depends on what? On the object or on the owner? Am I clear? :D