The Soviet archives are still very closed, and what's open is often not known in the West, so we can't make any strong argument from silence.

In this specific case, any Soviet examination or lack of examination is weaker evidence than it looks. The Soviets learned of the possibility & feasibility of h-bombs through spies, so they could have had access to this report or their spies' dismissal of the possibility (based on the report) or they could reason that the Americans who were sufficiently insightful to invent h-bombs (where they couldn't) were also insightful enough to check the safety issues.

Finally, given the general environmental fallout from all sorts of Soviet programs, it's not clear they ever cared about such issues very much. (For example, the Tsar Bomba was the result of a crash program for a political demonstration where the teams knew their designs and calculations were rushed & unreliable, and hence the bomb could have fizzled or been another Bikini Atoll or something. It was still detonated.)