Assign multiple Elastic IPs to EC2 instance

To communicate outside of the VPC, each non-default subnet needs a routing table and an internet gateway associated to it (the default subnets get an external gateway and a routing table by default).

Depending on the way you have created public subnet in the VPC, you might need to explicitly add them additionally. Your VPC setup sounds like it matches Scenario 1 - a private cloud (VPC) with a single public subnet, and an Internet gateway to enable communication over the Internet from the AWS VPC documentation.

You will need to add an internet gateway to your VPC and inside the Public subnet's routing table assign 0.0.0.0/0 (default route) to go to the assigned internet gateway. There is a nice illustration of the exact network topology inside the documentation.

Also, for more information, you can check the VPC Internet Gateway AWS documentation. Unfortunately it's a little messy and a non-obvious gotcha.

For more details about connection issues, see also: Troubleshooting Connecting to Your Instance.

Is there a way to assign the public elastic IP address directly to the eth0 interface?

No, there is not. Internet traffic to/from EC2 instances always traverse the Elastic IP 1:1 NAT infrastructure.

If not, does anyone know a work around to using Vyatta in a VPC configured with an ipsec VPN?

I have all manner of IPsec operating in VPC (including IPSec tunnels that cross NAT boundaries) without issue. Why do you think you need to have the public address directly assigned to the host? That is not a requirement from IPsec's perspective.