Not having been through an Alcohol treatment program myself; I am
curious to know whether or not there is any evidence that abstinence
from sex during the course of an outpatient program is typically
recommended - & if so, does doing so garner a stronger chance of
success for the patient?

Some of the folks in outpatient treatment are married or in long-term
committed relationships.  Seems to me quitting drinking/drugs would be
hard enough without asking a man (or woman) to give up sex too.  I was
married to a man that went to in-patient treatment followed by 2 years
of supervised out patient treatment.  I participated in all the
meetings in which I was invitied.  Sex was never an issue rasied by
the facillators in treatment (at all, ever), but abstinance from drugs
and alcohol WAS.

I know of no alcohol rehabilitation programs that require sexual
abstinence for those who are either married or in a long-term
committed relationships.  Alcohol rehab programs DO, however, often
require members to refrain from all sorts of "addictive" behavior. 
That would include behaviors such as excessive internet use, the
viewing of pornography, and sexual promiscuity.

The Common Sense answer is straighforward.   If you are SINGLE and
LOOKING, often that means going where there are others who are also
SINGLE and LOOKING.  And in today's world, that means clubs and bars
where alcohol is served.  For both heterosexuals and homosexuals, the
club scene can be quite dangerous once addiction to ethanol
(alcoholism) has become part of the picture.

In recovery, the issue is often making a permanent life-style change
that removes alcohol from one's life forever.  (AA advocates total,
life-long abstinence.  Other treatment modalities are less strict.) 
If the issue is life-long abstinence, then staying OUT of clubs and
bars is a MUST.

I went through a great program that changed my life and this wasn't an
issue as well. But they did not recommend going into new relationships
for some time because the potential stress related to that can be a
trigger for relapse. You can read more about this program at
http://www.drugrehabcenter.com