the reason the bombers were in the open is due to Russian compliance with the START treaty.

First, Russia suspended it’s participation in new START

Second, are you sure that’s a requirement of the treaty?

The only relevant article I could find is the following (emphasis mine):

Article X

1. For the purpose of ensuring verification of compliance with the provisions of this Treaty, each Party undertakes: (a) to use national technical means of verification at its disposal in a manner consistent with generally recognized principles of international law; (b) not to interfere with the national technical means of verification of the other Party operating in accordance with this Article; and © not to use concealment measures that impede verification, by national technical means of verification, of compliance with the provisions of this Treaty.
2. The obligation not to use concealment measures includes the obligation not to use them at test ranges, including measures that result in the concealment of ICBMs, SLBMs, ICBM launchers, or the association between ICBMs or SLBMs and their launchers during testing. The obligation not to use concealment measures shall not apply to cover or concealment practices at ICBM bases or to the use of environmental shelters for strategic offensive arms.

Looks to me like plane hangars are allowed while the tires on planes that they actually used are illegal as they don’t protect against the weather and just exist to fool bad satellite images.