Ive arranged to put my car on the rollers.

Before I do this im a bit concerned, my Subaru is pulling to the left a bit so I wanted to get the tracking done, I called up for garage and they told me the tracking is 4 wheel aligning. I thought 4 wheel alignment is something different?

Is there a risk of the car coming off the rollers?

 

The 4 wheel alignment is only part of it, they should also check for camber and toe together with steering alignment.

4 wheel alignment is probably a coloquial term used by the garage.

WRT coming off the rollers, I can't imagine that the alignment would be that bad to make it 'crab' off but I bet you would see a reduced power output so it's definitely worth getting sorted before the RR.

Do a search for the Prodrive settings and take those with you when you get the alignment done, this will assist with the car's handling.