Does the ulysses app have anything that is useful for creating placeholder text?
For instance, if I didn't have a character name, or a place name I could do:
{protagonist_first_name}
or
{placename_1}
And then just do a search and replace.
I just wondered if there was anything built in that made this process simpler. (Keyboard shortcuts etc.)
Ulysses does not support placeholders directly and there are no simple shortcuts that would create a placeholder.
You would have to use your own implementation. For things to keep track of when using such a custom method have a look at my answer to the question What should I do when I am stuck on names during freewriting? Depending on your language and your writing style you might get problems if you have for example nicknames or longer versions of a name and forget to change them. Or you could have problems with grammar rules.
Here you can see a list of features that Ulysses supports. The ones that might be useful for you would probably be to annotate your text with keywords and the classical Search&Replace.
Here is a list of available shortcuts.
To read more about keywords take a look at this article. Basically this feature allows you to add meta data to your work so that you could annotate the text with a special keyword indicating for example "Prog_First_Name_Missing". As keywords are reusable this should be quite easy and fast to do once you've got the hang of it. To add a keyword you can press "⇑ ⌘ K".
For Search&Replace you can press "⌥⌘F".
