Dimensionless Cloudwatch Metrics

The CloudWatch collection mechanism should work with dimensionless metrics - have you tried using the Poll Now feature?  You can see it on the raw data tab for the DataSource, and it should display any errors returned by AWS, as well as the request LM is making to AWS (so you can see if, e.g. the aggregation method is being incorrectly passed as a dimension).  We'll do some testing on our end to confirm data collection works for dimensionless metrics & put up an example in the docs.