is there a way to install fetchmail to use on this system so once you have setup a domain and email account you can use fetchmail and download other email into an inbox. if not is there an easy way to add this or should this be put in the feature request list.

this heavily depends on how fetchmail works.

in general,
With ehcp, you can install almost any application using apt-get install .... statement.
however, the way of working of that applicaton makes the sense.
If that application has no interference with ehcp configuration, then, you may directly use it. if some configuration is needed, then, you needed to do that.

lets come to fetchmail case:
as its site says: Fetchmail is a full-featured, robust, well-documented remote-mail retrieval and forwarding utility intended to be used over on-demand TCP/IP links (such as SLIP or PPP connections). It supports every remote-mail protocol now in use on the Internet: POP2, POP3, RPOP, APOP, KPOP .....

you may install fetchmail in your ubuntu using:
apt-get install fetchmail

however I am not sure what else required.. ehcp uses courier imap/pop3 daemons. and they are configured to work with mysql authentication (as configured by install_lib.php, look in that file if you are a programmer)
if fetchmail does same functionality with courier, you need to configure fetchmail in same manner. existence of both programs "may" interfere with each other.

these were my ideas.

as a result: if you are not a system engineer or programmer, there is no direct easy way to use fetchmail,
if you trust yourself, you can give a try.