If you live in a noisy area earplugs may be a requirement to shut yourself out from the hindering distractions, but they are by no means necessary.
It’s really your call, but if you’re having trouble relaxing do to noise, they would definitely help you meet your WILD goals more easily.
As for MILD, I’m not really sure. MILD is just like going to sleep regularly only with the added intent to remember you are dreaming and to realize you are dreaming. Granted, it is most effective after sleeping for a few hours and then waking up and going back to sleep, (a combination of WBTB and MILD is extremely effective) so if you have trouble falling back to sleep, again, due to noise, I suppose you could benefit from using earplugs, but remember it’s what you think will work best for you.