<p>Yes, that is the official advice and it is good advice. Although a candidate with an LOA only needs “a nomination”, and that requirement is met if a candidate has a service connected nomination (the OP said he already had such a nomination), having additional nominations gives admissions more leeway in how they allocate their appointments (ie the benefit is to admissions and other candidates rather than to the LOA recipient). If a LOA recipient does not have a nomination already he/she should definitely apply to every source available to him/her.</p>