Alex,
If speakers offer us copies of their slides, there’s no problem with putting them online, but be aware that many speakers are uncomfortable about this. At a recent conference I went to, less than a third of speakers were willing to share their slides.
There can be all sorts of reasons for this: they may plan to reuse the slides at future events, they may have shown figures or images that belong to other people, they may worry that people will steal their work, and professionals may have shown results that aren’t published yet.
If you do approach speakers about this (note that the web ops team has previously advised meeting organisers not to do so), I’d recommend going very gently, and making anything you receive accessible to members only.
Best wishes,
Dominic.