Can you give it a try like this?
$user='userid@company.net'
$pswd='password'
Import-Csv-Path .\Host.csv -UseCulture -PipelineVariable row |
ForEach-Object-Process {
$esx=Get-VMHost$row.host-ErrorAction SilentlyContinue
$result=''
if($esx){
$result=$esx.ExtensionData.Summary.Hardware.OtherIdentifyingInfo[0].IdentifierValue
}
$row|Add-Member-MemberType NoteProperty -Name 'result'-Value $result-PassThru
}|Export-Csv-Path .\servicetags-result.csv -NoTypeInformation