in refugee camps in other African and Arab countries
It is true what you stated as far as refugees, but those groups unfortunately coming from war torn or rebel areas in Darfur or southern parts of Sudan, so those groups make up some of the refugees you mentioned, and many of those groups come to Khartoum as well or migrant to other areas within Sudan in the North or near the Egyptian border. As far as Arab countries mainly in the Gulf, i am talking about North Sudanese now, before dubai became developed, the British assigned Northern Sudanese(educated) and some Egypt to set up their infrastructure, educate the locals, and military etc. So to bring them up to speed in the 20th century. So you always had a large Sudanese community in places such as Abu Dhabi, Dubai, Oman, and Saudi Arabia. Also since Sudan is part of the Arab league, you can migrant to other arab countries(mainly the Gulf" without major issues.
"The Sudanese community has been in the UAE since the late '60s and early '70s," said Salah el Din al Tayeb, the club secretary general. "The Sudanese were brought to the Trucial States by the British to manage the civil development of the different emirates. By the '70s and the formation of the UAE, the community grew and more doctors, officers and engineers were called to help build the UAE"
http://www.thenational.ae/news/uae-news/sudans-expats-still-club-together