The answer is yes! After a while trying to develop my own zimlet, I realized that it's possible (and even easy) to access all forms in Zimbra Administrator Console through zimlets! XFormObject is already defined since zimlets are being loaded after the relevant module was loaded (specially in dev mode). We just need to consider two things in our zimlet: 1-In Zimlet Definition File (The xml file), The extension must be true:
<zimlet name="com_zimbra_myzimlet" version="1.0" description="myform" extension="true">
2-we should introduce our Modifier function, and in the end, push that to the relevant ZaTabView.XFormModifiers array. in my case, ZaTabView.XFormModifiers["ZaAccountXFormView"].
ZaTabView.XFormModifiers["ZaAccountXFormView"].push(myfunction.AccountXFormModifier);
I hope you enjoy writing your zimlets on form extensions!