Wouldn't the inclusion, and wide usage, of both style and attribute params actually increase the ambiguity instead of resolving it. If we have two ways of accomplishing the same thing, then we would need to come up with a priority order, which may not be immediately obvious to the caller.

I guess it just falls back to the inherit precedence in the svg elements themselves.
Looking at this StackOverflow post the order seems to be:

Thus the precedence, from lowest to highest, is

1. attributes
2. CSS style sheets
3. inline styles

The reasoning that the post arrives at is that the choice to use attributes or styles comes down to whether it represents 'content' or 'style'

Looking at the LabelSeries it looks as though marginLeft and marginTop were only included at attributes because they are being used to set the translate

margin(Left|Right|Top|Bottom) are being passed by the XYPlot to all of the series so that they can properly offset themselves to account for the margins that are passed to the chart itself.

I think the other thing that we may want to consider, is how similar we want our svg and canvas apis?