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".