Actually, I don't know why you'd have to ask specifically about the USSR. Wouldn't the same question apply to any feudal-type government, where the king is in principle the owner of all of the land in the kingdom? And AFAIK there's no concept in halachah that you have to ask him for permission to build a sukkah.
I think the reason might be, building on zaq's comment:
All of the housing stock in the USSR (or in a feudal kingdom) may have been government-owned, but it was effectively leased to individuals to use for normal residential purposes. Well, a sukkah is, for us Jews, a normal residential purpose for the week of Sukkos (indeed, halachah considers the sukkah fully the equivalent of a normal house for purposes of civil law - see Sukkah 31a). One presumes, then, that the Communists would have had no particular objection to someone putting up a hut in their back yard just for relaxation or storage or whatever; the fact that they prohibited doing so for religious purposes is, of course, outside of the scope of dina d'malchusa dina.