So your ArcObjects code is calling an existing python script which is a script tool in a toolbox? You are not planning to port your python code into ArcObjects, simply call an existing script. This is what I understand you are asking? You would like to hook into the messages that are displayed if this tool was say run from ArcToolbox in ArcMap?
Well below is some VBA code that shows you how to call a standard tool from within ArcObjects code and actually show it's user interface, rather than executing the tool behind the scenes. This open up the dialog window for me so I could see all the scripting messages. This is one way to go?
Public Sub OpenCalculateTool()
' Hook into Toolbox and get the tool
Dim pUID As New UID
pUID = "esriGeoprocessingUI.ArcToolboxExtension"
Dim pArcToolboxExtension As IArcToolboxExtension
Set pArcToolboxExtension = Application.FindExtensionByCLSID(pUID)
Dim pArcToolbox As IArcToolbox
Set pArcToolbox = pArcToolboxExtension.ArcToolbox
Dim pGPTool As IGPTool
Set pGPTool = pArcToolbox.GetToolbyNameString("CalculateField")
' Create messages, required by Invoke method
Dim msgs As IGPMessages
Set msgs = New GPMessages
' Get existing parameter structure
Dim pArray As IArray
Set pArray = pGPTool.ParameterInfo
' Declare Parameter interfaces
Dim pGPParameter As IGPParameter
Dim pGPDataType As IGPDataType
Dim pGPParameterEdit As IGPParameterEdit
' Set the parameters of the tool
Set pGPParameter = pArray.Element(0)
Set pGPParameterEdit = pGPParameter
Set pGPDataType = pGPParameter.DataType
Set pGPParameterEdit.Value = pGPDataType.CreateValue("a") ' Featurelayer name
Set pGPParameter = pArray.Element(1)
Set pGPParameterEdit = pGPParameter
Set pGPDataType = pGPParameter.DataType
Set pGPParameterEdit.Value = pGPDataType.CreateValue("xx") ' Field
Set pGPParameter = pArray.Element(3)
Set pGPParameterEdit = pGPParameter
Set pGPDataType = pGPParameter.DataType
Set pGPParameterEdit.Value = pGPDataType.CreateValue("VB")
' Open the tool
Dim pGPToolCommandHelper As IGPToolCommandHelper2
Set pGPToolCommandHelper = New GPToolCommandHelper
pGPToolCommandHelper.SetTool pGPTool
pGPToolCommandHelper.InvokeModal 0, pArray, True, msgs
End Sub