First of all, the hash symbol is used to identify a location within the current document to which you want to seek, so using it to denote an endpoint on the server is semantically incorrect.

You should use query parameters for it instead of resorting to using the hash. For example, http://sub.domain.com/api/$metadata?endpoint=EndPointName

As far as I know, stripping the hash sign is angular's implementation of the Http module

I found this:

Fragment Parameters The fragment part of the URL, everything after a hash symbol, is information that is normally used only by the client, such as a browser, and not processed by the server. Therefore it is uninteresting when discussing REST parameters. The only interesting item is if you need to send the actual hash character as a value (instead of representing the hash control symbol) to one of the options. In that case you need to encode the URL.

Character Encoding Special characters are encoded in the URL, by a mechanism called “percent encoding”. In this mechanism any character can be replaced by the percent symbol, followed by a two-digit hexadecimal value of the encoded character. If special characters (such as the hash character) need to be sent as actual data, they must be encoded. All other characters can optionally be encoded.

Here: https://www.soapui.org/testing-dojo/best-practices/understanding-rest-headers-and-parameters.html