Okura Frontier is near a shopping mall, cinemas etc. which probably makes it the most "exciting" location in a very bland, suburban region.

It is also within walking distance of three railway stations (JR, Odakyu and Sotetsu) so you have good access to Zama and to Yokohama (which is a good place to go for Chinese food / beers in a lively, urban setting when the sheer dullness of Ebina drives them to despair).
http://www.okura-ebina.co.jp/loca1.html

Okura has a call center in the US that might be able to answer any questions you have:
http://www.okura-ebina.co.jp/OFE_Fact_E.pdf

The most convenient station for Camp Zama is actually Sobudaishita. It's on the JR line, two stops from JR Ebina station. (So don't take the Odakyu line to Zama - take the JR line to Sobudaishita instead).

I guess the hotel might be able to arrange for a six person taxi or van to take them to Camp Zama too.

If they join the Okura club, they may qualify for a discount. (The points don't add up to much in the way of benefits, though).
http://www.okura.com/oci/