As to my knowledge, the MT4 plugin corrects the time zone with the "BrokerTime" function. This function is only called for the main broker. That's why additional MT4 brokers got no time zone shift for their historical data. This has nothing to do with "SymbolTrade".
The BrokerTime function is now always called when historical data is requested from MT4, which is supposed to enforce the time zone shift. If you have still a problem, or some other problem, please contact Support with details.