Cerberus Capital Management LP is interested in acquiring full ownership of GMAC Financial Services in potentially far-reaching discussions with General Motors Corp. that could involve a merger of two of Detroit's three automakers, according to sources familiar with the talks.But analysts and industry executives were highly skeptical of any deal involving a merger of GM's automotive operations with those of Chrysler LLC.'If this were to take place, the winner would be Cerberus,' which would benefit by combining the financial operations, said Maryann Keller, a longtime analyst and head of Maryann Keller & Associates in Stamford, Conn.