Yes I think it will be working fine in Production. It could be just a context issue. Those kind of activities are configured to work within a specific context (parameters, primary pages, step pages) but if said context is correct that should be working perfectly in Production as well
SendSimpleEmail Activity is called when we refer the "SendEmail" smart shape and it is used when we refer the shape in flow and pass the parameters. Meanwhile , what pega might be implying is , if we want to use same logic in Utility to send Email , we should Call-CorrNew, could see this rule marked as Utility.Anyhow , in Production , using any of these, sends Email while generating the Production because of both of them calls CorrSend finally.