Well, as far as I know most men would be ok with receiving unsolicited nudes from strangers or people they know (given it is the sex they are attracted to sending it), SPECIALLY in a app used for dating where if you get a match it means both feel attracted to each other somehow.
Women on the other hand seem to generally not like to see nudes unless they ask for it or if the conversation induces it (which can be complicated to be sure given how difficult, specially for most men, to know the actual intentions in a conversion sometimes, but that is another subject), so they are generally put off by receiving this kind of content.
I think there is a big disconnection in behavior and people generally do to others what they would like to be done to them, instead of thinking what the other would like to be done to them, in this case a lot of men would like to exchange nudes almost immediately, so it is what they do, thinking that would get the other party just as excited as it would made them.
I really would like to know how this behavior is on same sex dating apps, if it is generally accepted nudes in the first messages or if there is more conversion before closes came off and flashes come in?