My ony serious Aikido injury was to my shoulder, during a vigorous randori. It was a number 4 in Erik's typology
"Uke is moving to fast. Like Klickstein said "If you can only do ukemi at 7mph dont attack at 70mph!""
During the same time I've been doing Aikido, I've had two similar-intensity injuries from telemarking (skiing) -- sprained thumb and twisted ankle. So, from my personal experience, I'd go with Aikido being safer than skiing.