In principle, it may be (and most probably is) illegal to collect personal information and ID data this way.
As a minimum, serious responsibility is applied to collecting, storing, and processing this type of data. When you collect this data over guest WiFi (it has no encryption), data are open to everybody to collect, so they are in fact made publicly available. In case of any problem, you as an owner of the network with such setup are responsible.You also are obliged to put clear warning, that inputting the ID info in the form over this insecure setup, users as well as publish them on Internet. You also must state why you collect this data and for what use you collect them.
Do you really want that? I don't think so. Anyway, for what legitimate goal would you want to collect personal ID numbers? Difficult to imagine...
Better think twice, if you really need that...
Also, I personally would avoid any WiFi network asking for such data, as it looks very suspicious, and I definitely would never input my personal data in such form. Only legitimate reason for asking for such data is signing some service agreement or making a payment, and in this case it must be done over SSL encrypted connection to a reputable service provider, and no other way.
