If you use the --ipa option to ipsilon-server-install it will fail with obscure stacktraces due to missing ipa components.

[2015-01-04 10:21:42,130] Configuring environment helpers                       
[2015-01-04 10:21:43,464] [Errno 2] No such file or directory                   
Traceback (most recent call last):                                              
  File "/usr/sbin/ipsilon-server-install", line 336, in <module>                
    install(fplugins, opts)                                                     
  File "/usr/sbin/ipsilon-server-install", line 180, in install                 
    plugin.configure_server(args)                                               
  File "/usr/lib/python2.7/site-packages/ipsilon/helpers/ipa.py", line 176, in \
configure_server                                                                
    self.get_keytab(opts)                                                       
  File "/usr/lib/python2.7/site-packages/ipsilon/helpers/ipa.py", line 140, in \
get_keytab                                                                      
    stderr=subprocess.STDOUT)                                                   
  File "/usr/lib64/python2.7/subprocess.py", line 566, in check_output          
    process = Popen(stdout=PIPE, *popenargs, **kwargs)                          
  File "/usr/lib64/python2.7/subprocess.py", line 710, in __init__              
    errread, errwrite)                                                          
  File "/usr/lib64/python2.7/subprocess.py", line 1327, in _execute_child       
    raise child_exception                                                       
OSError: [Errno 2] No such file or directory    

It's obvious that one needs freeipa-client installed (but there is no dependency on it), but also needs freeipa-admintools installed, a less obvious requirement. 

However since ipa support is optional the main ipsilon package should not require it. This means ipsilon should have a ipa subpackage with it's own dependencies.

Also note that the names of the dependent ipa packages differ between Fedora and RHEL.