It is usually possible to look into someone's VOMS server and see 
who are considered members using a web browser with a certificate.

VOMS servers are web-services protected by GSI security.  Hence a grid 
certificate is needed to authenticate with the web-service.  Unless you 
know otherwise this condition rules out wget and curl.  Once 
authenticated the rules are pretty loose on who can view the members of 
the VO.  Under OSG, any certificate issued by DOEGrids can view the 
contents of the VO.  I can't speak to LCG/Nordugrid but I know one can 
inspect the ATLAS VO server.

Here are the general rules that I use:  Feel free to test these against 
DOSAR's VOMS

1) Get the URL of the voms server:
    You can derive these from the entries in edg-mkgridmap.conf file 
distributed with OSG.  Simply change "vomss://" to "https://" and 
remember that the entry contains the mapping to the local account (last 
word).  e.g:

group vomss://voms.fnal.gov:8443/voms/des?/des/production des

The URL is:

https://voms.fnal.gov:8443/voms/des?/des/production

2)  Put the URL into a browser containing your certificate
     You should probably arrive at the top web-page for the VO. This has 
worked for the handful of tests against OSG VOMS servers I just tried

3) On the left menu bar, there should be an entry for "Administer the 
VO" or "Adminstrate VOMS".  Click on this.  The difference in the link 
is dependent on which version of VomsAdmin is running on the server.

4) On the resulting page you should see either a "Users" or "List Users" 
on the left menu bar.  Clicking this should provide the list of all 
members regardless of roles or groups.

5) You can use the menu items under the administration page to see group 
and role information as well.

Thanks to Patrick McGuigan for this info.