I've accidentally bought an inner tube with a Schrader valve for a bicycle that's currently fitted with Dunlop valves. Can I still use it or they require holes in the rim of a different size?
Answer: Yes you can. Woods/Dunlop valves have a nominal hole size of 8mm, identical to a Schrader/Auto valve.
For completeness, a presta valve uses a 6mm hole.
Reasons not to - authenticity of an antique bike, or maybe having to carry a second pump head/fitting if both tubes have different valves.