As a filmmaker, a lot of my work can be seen on youtube. Do agents take video links as a way of examining the works of a writer/producer/director? Examining the work someone has made before can cut thru the glut of someone sending a screenplay or query letter? Of course there will be mistakes here and there but talent in conception can be evaluated, do you think?
I highly doubt it, UNLESS there is already a buzz about that filmmaker. Typically you will gain some level of acclaim through various avenues, and then agents/producers will take notice. The good ones are so innundated with talent they don't need to browse around the web for more.