I currently use a repeating pattern of raster images on one of my websites, which isn't so complex that it couldn't be converted to vector, but hasn't, as of yet, been scaled up to look decent on HiDPI/Retina displays.
I'm considering converting the raster pattern to vector, and setting the resulting .svg
image as the background, but I want to know whether there are any disadvantages to using vector images in a website background.
But I strongly believe that vector graphics have much more advantages than disadvantages, so go for it.