If a party files an ex parte, is it common for the attorney to be the only declaration attached to the application?

If the declaration contains the requisite information necessary for the court and pursuant to the rules of court requiring a declaration of necessity, an attorney declaration could be sufficient. unfortunately, much more information is necessary in order to determine what is sufficient for an emergency in any given circumstance. There are specific rules of court and statutes regarding ex parte applications.

Your question cannot be answered from this sparse information. Never assume that your opposing attorney or judge is incompetent.

Ex Parte application for what relief? Whether the application needs a declaration from the party as well as his/her attorney depends in large part on what relief is being sought and whether the attorney's declaration and the attached exhibits provide the court with sufficient information to rule on the ex parte application. As you do not say what the motion is for, it's not possible to provide a more meaningful response to your question. Sorry.