They're similar to scissor trusses. BTW, all RORs should be done with scissor trusses. They give you more headroom and you can get away with shorter walls. Shorter walls mean more horizon and better leverage in rolling off the roof.
Yes, open roof rafters like BYO have built you are plenty strong enough for a small or midsize observatory, the end framing is totally sufficient to keep the roof from pancaking on a roof that short. An easily installed upgrade, for slightly larger roofs, or ones with significant snow loads, is to add 'collar-ties' up close to the peak. A collar tie half-way down a rafter is (if I remember right) 90% as strong as one at the base of the rafters...and offers significantly more headroom.
Overall, my sincere compliments to the BYO crew, they do a thouroughly professional job with their observatories,.....I've been a carpenter my whole life, I can spot right off the difference between good enough and good....those folks do DARN good work! They could put about half as much lumber in there, and the building would still stand up.....