Are you running On-Demand Scans at all? If you are i would check to see if you have the Run if Missed option checked, this would cause the scan to initiate within the specified timeframe and will impact a user when logging in.
The application you referenced i am assuming that the On-Access Scanner (OAS) is the one that is causing the performance issue, and yes you can exclude the application from being scanned. You can verify this by reviewing the logs on the local system \Program Data\McAfee\DesktopProtection
OAS - Exclusion
Policy Catalog > VirusScan Enterprise 8.8.0 > On-Access Default processes Policies
Edit the policy for the system in question
From the "Settings for" ensure that its set for the correct system type (Workstation or Server)
Click the Exclusions tab
Within the "What not to scan" box you can ADD a new exclusion and specify either the path or the executable.