USA: DSE will only be treated as regular high school coursework with NO credit granted in college (and hence unfortunately is unfavorable compared to IB/AP/GCE); all applicants must submit SAT/ACT as standardized testing. TOEFL iBT also mandatory for DSE candidates
DSE English (as distinguished from English Literature) is definitely not equivalent to an A2 level subject of GCE and I doubt it is even upto AS level. I think normally UK U's only consider it as evidence of competence in English, like IELTS, but not as one of the 3 required A-level subjects.