The following article refers to functionality available in Workflow builder, which can be accessed in one of the following locations, depending on your configuration:

Administration > HR > Workflows 
or
Administration > HR > Workflows > Workflows

Within Workflow Builder it is now possible to determine whether the workflow will trigger for employees who are currently in probation. 

When building a workflow, you will see the following option: 

This setting will determine whether or not a workflow will trigger against an employee based on their probation date in the system. The probation date for an employee is set on their file in:

People > Employees 

On the employee's card click on the Change icon under the Core Details Heading:

And locate the Probationary date setting:

Depending on the option chosen and the probationary date value for the employee will determine how this option works - see below for all the possible outcomes where the workflow will or will not trigger:

Please pay particular attention to how blank / no probationary date is dealt with - depending on the option chosen this can behave very differently.