You can use multiple Entity objects, but since you can only assign one model per view, a tabbed UI is still a single form, it just hides tabbed elements until an event makes them visible. So, at the top of any view that calls a model, you'll be familiar with this:
@model Web.Project.Name.Models.ViewModel
However, you can use partial views on each of your tabs to invoke the model you want the user to interact with, because partial views can have their own models. In this way, each tab effectively becomes its own form. Your main page(sans a layout view):
@model Web.Project.Name.Models
@{Viewbag.Title = "Orders & Customers";}
...
<div class="tab-1">
@Html.Partial("_OrdersPartial")
</div>
<div class="tab-2">
@Html.Partial("_CustomersPartial")
</div>
Those partials you're loading would each have their own model:
_OrdersPartial.cshtml:
@model Web.Project.Name.Models.OrdersViewModel
@{Viewbag.Title = "Orders & Customers";}
...
In this case, the user interaction with each tab and its partial view will handle each tab as its own form, which is effectively is. It's also important to note that you don't really even need more than one Entity objects to create different models. You can use Entity framework to create multiple models from the same DB.