Tarps are very cheap compared too what is spent at that base. If you're going too hide a capability then you're not going camouflage it with a greenhouse where the enemy can see the size, shape and planform. Remember the Russians figured out the a12 from its heat shadows from the pole model cast onto the sand? the greenhouse isn't even fogged glass..... The number if things wrong with this whole entire scenario is like 100 things wrong to 1 thing even remotely right.1. Even if it is light transparent doesn‘t mean you can take picture from it. I bet you will be not able to recognize anything outside that is more than 50m.
2. Hangar block view to the south from temp hangar - so you are not able to see what is landing or starting.
3. It is most remote location in Area51 with access to the runway and concrete pad. I do not see any better place to put broken Draken for repair. Main complex is screened with closed entry, other side protected by another hangar. Also hangar make sense as you can deliver repair crew inside temp structure. They just see what they need and nothing more.
I can imagine 40 years ago when the f117'was coming on line... "Hey guys lets hide them under a transparent greenhouse when the sats pass over."