edgemoron:
If the transistor is not fully saturated it will be acting like a variable resistor instead of a full on switch and may overheat, also, if the relay coil is not getting enough hold in current, it could drop out with a hard mechanical shock, I wouldn't use the second R, nor second guess the module designer.
Thanks Edge!
So.. another question arises 
The module was not designed for 3.3v (It´s for 5v. VCC and ground are going to 5v, but signal is triggered by a ESP high state pin.) So, how can I know if the transistor is fully saturated? Maybe measuring voltage across base and ground?
I dont want to blow the smc transitor!
BTW: I´m planning to use this circuit to trigger my central heating "thermostat" input, by closing a (I think) 30v DC standard thermostat circuit. Do you recommend a solid state component such as a mosfet, etc.?
Cheers!