But i can connect that pin 85 (relay gnd) to vems to turn on fuel pump? It wont kill p259 or something i hope.
You need to use a suppressed relay, either a resistor or diode that bridges the +ve and -ve of the coil. Otherwise you risk damaging the P259 chip.
Other than this the relay will not damage the Vems unit. Avoid any sort of dead short as this will surely kill the chip, so be double sure your wiring is right, which goes without saying with any wiring.
Edit** just realised you intend to use IGTB, in which case the relay does not need to be suppressed. Your last comment one the p259 chip confused things a little