Do I need a heated line and /or a gas conditioning unit to measure SO2 and NO2 accurately?

Both SO2 and in particular NO2 are soluble in water. The use of a heated line and a gas conditioner virtually eliminate the time that the sample gas is exposed to water and results in negligible sample loss. The down side is that the equipment is expensive and bulky.

For short term spot checks it is more convenient to use a fluoroplastic lined hose and a high speed pump so that there is minimal hang-up in the hose and contact time with any moisture is minimised.