To answer your second question first...
Being recruited for a DIII sport is A LOT different than being recruited for a DI sport -- not just at Hopkins. DI coaches have much more pull, and scholarships are involved as well.
As far as your first question, tt never hurts to get in touch with a coach if you are possibly interested in playing a DIII sport at Hopkins. Just send them an email with questions about the team and also an introduction of yourself and your abilities. Coach contact info can be found here:
http://hopkinssports.cstv.com/school...hop-staff.html
Admissions works closely with all the coaches and a supported recruit will be factored in the Admissions review process. Being a recruit will matter, but how much of a factor depends on where you rank on a coach's list and also how strong of a candidate you are for admissions.