I don’t know of a source explaining why he chose this artist name. It does seem to be his real name according to the japanese wikipedia article (本名: 新井 圭一), however the kanji do not dictate the use of ゐ over い. So it’s most likely an artistic consideration (as does happen often with artist/stage names). He chose to use a hiragana version over the usual kanji version to begin with, which could also be done for style.