If I setup Weather Display to grab data from my WLL, Would WLL still send data to weatherlink cloud?
Yes is the basic answer. There's a slight caveat in that WLL is obviously a pretty new product and I'm not sure how extensively WD will have been tested with WLL as yet but I wouldn't expect there to be any issues.
NB Can I just quibble with 'WDL' in the subject. Weather Display is usually abbreviated WD. WDL is something else, ie Weather Display
Live, but which is rapidly falling out of favour because it uses Flash. I suspect you just mean WD and not WDL (WD is what would do the polling of WLL anyway and not WDL), but it just helps to avoid confusion to stick to the normal usage of the abbreviations.