You should not calculate your distance to swim start based off the Westin. You're going to be at transition area early in the morning anyways. It's exactly 1 mile from transition to swim start along the waterway.

I have stayed there in the past and walk and am doing so again this year. Everybody walks. It is a short walk to transition like mentioned above. Get your bike set up then follow the crowd to the swim start. It really isn't a bad walk. Part of the IMTX experience.