nope

class MarkupInlineWidget(MultiWidget):
    def __init__(self, attrs=None):
        _widgets = (
            AdminMarkupTextareaWidget(),
            InlineWidget(),
        )
        super(MarkupInlineWidget, self).__init__(_widgets, attrs)

    def decompress(self, value):
        if value:
            return [value]
        return [None]

yep

class MarkupInlineWidget(InlineWidget, AdminMarkupTextareaWidget):
    pass