As far as I am aware, it's frowned apon to analyse external conflicting perspectives, i.e. two sides across two different texts, as oposed to a self contained one, so firstly make sure your analysis is integrated, yet one does not depend on the other.
My advice would be to look for similarities (or contrasts) in methodology, themes, etc. For instance, both poems mention 'white' alot, and use it as a metaphor for fear.
A big thing I thought would go well with those two poems is the idea that differing contexts, mindsets and interperetations of the same facts lead to differing perspectives.
You could argue that the conflicting perspectives of Hughes' poem and it's close relationship with Plath's encourages the responder to view Plath's portrayal with skepticism. - It's important (IMO) to relate author intention to author action.
Good luck with your analysis!