Earbuds/headphones are meant to discourage approaches. They do that well. If you want to approach on a general gym floor now, you're likely going to need to approach someone wearing earbuds/headphones. Walking/hiking paths are getting that way too + you're competing with a woman's dog in a lot of cases. Millennials (1982-1996 births) are well known to be the most pet crazed generation ever. Single, unattached women are more likely to be pet owners than single, unattched men. Dogs are possible cocck blocks too as the woman may be less attentive to the approach. I would say that earbuds/headphones are a bigger discourager of approaches than a dog, though the combination of the two factors make outdoor approaching more difficult.
Yes, earbuds/headphones will affect an outcome negatively. When you approach someone with wearing those, they are already annoyed that you disrupted them. It becomes interruptive marketing rather than permissive marketing, unless you happen to get a good IOI from someone wearing earbuds/headphones, which isn't that common.