As far as I know, no, they don't test for that.  I did a 5-panel pre-employment screening about 2 years ago, and it was for marijuana, cocaine, opiates, methamphetamine and PCP.  Some places call for an expanded testing (10-panel), which also includes ecstasy, oxycodone, alcohol, methadone, prophoxyphene, barbiturates, and benzodiazepines.  I have not seen any labs that test for psilocybin, and I believe in previous discussions here, the overall consensus was that it is not done as a routine matter.

Thank you!!

I just realized that we are standing on the next cycle's doorstep.  It seemed longer because the last one, in 2006, was cut short by using the mushrooms. (His go in 3-3.5yr cycles)  The relief was HUGE!  I want him to be able to use that method again if necessary, but do not want him to put this new job at risk.  It's the key to our future.

Thanks again for the responses!

Mat wrote on Nov 6^th, 2009 at 3:35pm:

I'm pretty sure it's detectable in both the urine and in hair, but the process costs hundreds of dollars. I think it's gone from the urine in a matter of just a couple of days, but sticks around in the hair for up to a month.

These days the employer has to specifically dictate which drugs to test for.  There are so many different drugs.  You cant really ask the lab to test for 'all drugs' as it will take a huge amount of urine and a very high expense. 
Most testing labs offer a basic 12 or so drugs which are the most common.  It is not likely that LSD or mushrooms are on that list.
That being said, I believe Mat is correct.  Within 48 hours he should be clean as a whistle.