From my understanding, most drama schools (those that are accredited by the NCDT/CDS, at least) prefer that you perform your speeches in your natural accent. Some may even explicitly state this in their audition guidelines. The emphasis will be placed primarily on your ability to interpret the speech, whether it be emphasizing on certain words, your body language and/or poise. If you feel that the accent would enhance your performance, by all means employ it. Just be very aware that if you do, the accent needs to be spot on (i.e. authentic), otherwise it could potentially work against you. Moreover, as mentioned, some drama schools actually discourage the use of accents, preferring your own. Good luck.