My client was an asylum seeker receiving NASS support. In September he was granted indefinate leave to remain (outside the immigration rules on compassionate grounds). Can he apply for DLA or does the 26 week presence and ordinary resident test also require that you have not been subject to immigration control during that time as well?

Yes, it does. Regulation 2 DLA Regs defines residence and presence and includes, at sub para 2(1)(a)(ib):

"he is not a person subject to immigration control within the meaning of section 115(9) of the Immigration and Asylum Act 1999 or section 115 of that Act does not apply to him for the purposes of entitlement to disability living allowance by virtue of regulation 2 of the social security (immigration and asylum) consequential amendments regulations 2000..."