Short answer.... no impact.
Whilst luup.timezone might not be populated, luup.is_night doesn't depend upon it to "work out" whether it's in the Sunset->Sunrise time window. Most of the "luup." constructs are written directly in C, with no intermediate Lua dependancies, so it's not generally a problem as they can source the TZ data from elsewhere in your Vera system.
...unless, of course, you actually want the timezone offset value itself for some reason, then you'd be hosed.