You should read the manufactures instruction to find out if you require permenent ventilation. If its an open flued boiler then you will certainally need ventilation. If its a room sealed boiler then you may not require them. If you do need it and are going to put vents in the cupboard door don't forget that you will still need to put vents in a wall that communicates direct to outside. If you can and if the boiler requires them i would put the vent in the wall inside the cupboard iin which the boiler is located. If you do not have the manufactures instructions try locating them on the internet or contact the makers technical help line.
Bob the plumber, February 2009