Here's a post from their facebook page suggesting it's probably not taken into consideration if sent.
From 1/9/2013 on fb
Hello All,
We sometimes receive letters from applicants expressing their intention of matriculating at Hopkins should they be accepted. Some medical schools may encourage this type of letter, but they really mean very little to our Admissions Committee. The reason is that we assume that anyone who applies may initially intend to enroll, otherwise why apply? A letter that we welcome is the one sent along with an acceptance offer. Some schools call these letters of intent, statement if intent and I have also seen them referred to as a declaration of intent. These must be returned to the medical school within a given period of time (it may vary, depending on the institution). It obligates the medical school to hold the admitted student's place in the class. The applicant, who may receive and accept multiple offers, is not obligated to any one school until May 15th, when he or she must withdraw all offers, save one. You may learn more about this on the AMCAS website.