I walk a few dogs who don't get daily walks for various reasons - mainly the owners' health.
If they're kept company at home, have a garden and are given plenty of mental stimulation, they're generally okay, if a bit giddy on walks 🙈
But I also think that the people who hire a dog walker aren't the kind of people to not walk their dogs, iyswim. I'm there as an addition while they're working, or to provide socialisation and company, not because that's the only time the dog gets out.
I hope that makes sense!