AWS .NET SimpleDB uses https

So do not be afraid. You are secure.
Declaring Type: Amazon.SimpleDB.AmazonSimpleDBConfig
Assembly: AWSSDK, Version=1.3.8.0

public AmazonSimpleDBConfig()
{
    this.serviceVersion = "2009-04-15";
    this.serviceURL = "https://sdb.amazonaws.com";
    this.userAgent = AWSSDKUtils.SDKUserAgent;
    this.signatureVersion = "2";
    this.signatureMethod = "HmacSHA256";
    this.proxyPort = -1;
    this.maxErrorRetry = 3;
    this.fUseSecureString = true;
}