The way I look at it is if you are on a trail with the Blazer Bash group you need to register yourself and any passengers because you are all going to count against the permit fee. If you're not going to be on a trail with the group, then I would encourage you to register as a guest. This helps with a count for the BBQ and helps support the event. There are some fixed costs like insurance and permit minimums that have to paid regardless of how many people are on a trail run. Heck even if you're not going to Blazer Bash you could purchase a passenger registration just to help out with the event costs.