Yes, it is possible for either partner to become infected with HIV through performing or receiving oral sex.
If the person receiving oral sex has HIV, their blood, semen (cum), pre-seminal fluid (pre-cum), or vaginal fluid may contain the virus. Cells lining the mouth of the person performing oral sex may allow HIV to enter their body.
The risk of HIV transmission increases
if the person performing oral sex has cuts or sores around or in their mouth or throat;
if the person receiving oral sex ejaculates in the mouth of the person performing oral sex; or
if the person receiving oral sex has another sexually transmitted disease (STD).
source:
http://www.cdc.gov/hiv/resources/qa/qa19.htm (Center for Disease Control and Prevention)