That is my concern as well. We are still running CentOS 6.4 which does not have the affected version of OpenSSL, but we terminate SSL at the ELB so if they are affected then are keys are not safe.
The forum thread has just been updated with this reply:
"We can confirm that load balancers using Elastic Load Balancing SSL termination are vulnerable to the Heartbleed Bug (CVE-2014-0160) reported earlier today. We are currently working to mitigate the impact of this issue and will provide further updates."
Edit: I've posted on the support forum, hopefully they get back to us https://forums.aws.amazon.com/thread.jspa?threadID=149690