Having looked more closely at the CommandBarButton, in my view there has been an ommision.
The CommandBarButton has all the normal properties of a RadButton or other items that allow an Image and Text to be set. For example, you can set a TextImageRelation etc.. But, in a RadButton you can normally set a DisplayStyle
which tells the control if it should render as Text, Image or Both. the DisplayStyle is not part of the CommandBarButton and I think it should be there. this link
indicates text and image can be combined.
If you want a text only button there is a simple way around it, which also answers your second question on using a host item.
You can add a host item in the same way as you add other items to the Command Bar, but the host item is just a placeholder, ready for you to add a RadElement to it. So, to add a RadButtonElement with just text on to the RadCommandBar, then you can do the following
button.DisplayStyle = DisplayStyle.Text
.CommandBarHostItem1.HostedItem = button.ButtonElement
I hope this helps, but let me know if you need more information