SQL Server 2012 SQL Agent Job with PowerShell step fails on Out-File cmdlet with "ReportWrongProviderType" error
The problem is that the PowerShell session is using the SqlServer provider by default. I added this statement into the script before the Out-File cmdlet:

Set-Location c:


This changed the provider to the FileSystem provider, and allowed the Out-File cmdlet to correctly find the file share and create the file.

This article contrasts how SQLPS loads in SQL Server 2008 R2 vs. SQL Server 2012/2014. The SQL Provider is loaded using the 'Add-PSSnapin' cmdlet in SQL Server 2008 R2,  while starting with SQL Server 2012, the 'Import-Module' cmdlet is used. 

The author states: "The outcome of loading the module [with 'Import-Module'] is simply changing to the PSDrive you just loaded." Evidently, the 'Add-PSSnapin' cmdlet left the provider for its SQLPS session unchanged (as FileSystem). That change in cmdlet use, and the resulting session behavior, was what caused my problem.