It's not as clear as that. Maybe yes, maybe no.
The PASE database, which is among the most cautious of all indexes to primary records, says that King Alfred's will devised seven manors to his brother's son Aethelhelm, and that this might be the same Aethelhelm who was Ealdorman of Wiltshire.
http://www.pase.ac.uk/pdb?dosp=VIEW_RECORDS&st=PERSON_NAME&...
These manors were supposed to descend in the male line of Aethelhelm, in the female line in the event of the failure of the male line, and to the nearest kin of King Alfred on the failure of both lines. One of these manors, Crondall is known to have been held by a son of Aethelhelm the ealdorman. Another of these manors, Compton in Surrey, can be traced much further, to Wulfroth Cild, the father of King Godwin.
If Aethelhelm the ealdorman was the same person as Aethelhelm the uncle of King Alfred, it would also explain how Aethelweard the Historian was "atavus" of King Alfred's 2nd great granddaughter Mathilda of Quedlingburg.
English Wikipedia mentions the idea the men are the same (which is accepted by many historians), then notes that historian Barbara Yorke rejected the identification, saying that it does not seem to have been the practice for English princes to be ealdormen. Buried in the Wikipedia footnotes is a documented example of another prince, Æthelbald, who was appointed an ealdorman in 850.
Before we go further along this line, it might be worth reading the analysis of Todd Farmerie:
https://groups.google.com/forum/#!msg/soc.genealogy.medieval/f2IloS...
