I have managed to connect a trial of untangle IPSEC to AWS VPC successfully.

The issue with AWS VPC is that it is not configurable but requires aes128 for phase one and a time out of 1hour on the SA. These items are not configurable in the ipsec interface.

The default encryption protocol is phase 1 from Untangle is 3DES and there is not an easy way to change it.
To connect to AWS create the tunnel as best you can in the web interface and save it.
Then open an ssh session to Untangle.
edit /etc/ipsec.conf with vi or nano
find the section containing the parameters for your aws tunnel
add the two lines below. I put these right above pfs=yes
ike=aes128-sha1-modp1024
esp=aes128-sha1

Then change salifetime to 1h.

Save the file and restart ipsec from the command line.

/etc/init.d/ipsec restart

This should bring the tunnel up.
You can use the ipsec log viewer to see if there are any errors.
Note that if you edit the tunnel in the interface or reboot the firewall these changes will be over written.
There are ways to prevent this but I doubt they are supported or recommended.

Cheers.
Matt