Would the safety bar squat be a good alternative for the high bar back squat?
I’m starting the Hypertrophy 1.0 template. I’ve never high bar squatted.
Long-term I plan to do powerlifting competition. So I don’t see the harm in safety squatting since competitions are not happening due to the COVID.
Sure, that works.
Kind of an aside, here…
My future plans include signing up for one of your 2-day seminars this year (hopefully, Chicago). Due to horrible shoulder inflexibility, I only squat with a Safety Squat Bar. Is SSB availability based on the equipment at the seminar location? If no SSB, do you allow time for stretching? Thanks in advance and hope to see you guys in the fall! 
Yep, based on whatever is available at the seminar venue. You are free to do whatever stretching is needed, and we can accommodate with other squat variations if needed as well.
Looking forward to meeting you.