The following information will clear all your doubts regarding IGNOU being AICTE approved:
IGNOU is not only a central university but also a nodal body to regulate distance education in India.
IGNOU can commence any course, even technical courses without or with approval of AICTE since it has the right to do so as per its constitution.
IGNOU has its own SOET (school of engineering and technology) duly approved by HRD and UGC. Their degrees and diplomas are equivalent to any other technical system in India.
AICTE never recognizes any degree/diploma in distance courses and hence it should be clearly understood for any institution. Nonetheless, IGNOU courses are themselves valid.
However, through a joint resolution of DEC(IGNOU) and AICTE, IGNOU is no longer offering any technical degree/diploma and neither recognizes other universities in DEC mode.