Actually, it looks like the overlapping datepicker appears as a result of the form-control class from the original input being applied to the widget span.
"k-widget k-datepicker k-header form-control"
Removing the form-control from the span corrects the appearance of the datepicker. Is there any way to indicate on a per-widget basis whether to apply the classes from the original element? I'm just concerned any solution at this point will be a big hack.