Of course you should introduce yourself to them and talk to them.
If someone was going to walk out in front of a car wouldn't you say something?

It's easy, just go over and introduce yourself, give them your phone number in case they need to contact you about anything (prowler) and take them some cookies or a bottle of wine.

Talk to them about their septic system - they may not be familiar with aerobic system.... and then mention that it smells really bad and probably needs service since it' s been vacant so long. Let them know it shouldn't smell like that when it's working properly.

Also warn them about their garden.

If you make it about being concerned for them - instead of how you are inconvenienced-- they will still get the idea, but it will be much better received.