The "$Host" variable is system reserved so you cannot overwrite it.
Your code updated:
$HostList = Import-Csv Hostprofiles.csv
Connect-VIServer -Server VIRTUALCENTER.DOMAIN.local -User "qa\a-dubutcher" -Password MYPASSWORD
# Apply host profile to all the VMs in $HostList
foreach($VMHost in $HostList) {
Apply-VMHostProfile -Entity $($VMHost.NAME) -Profile YKFProfile -Confirm:$false
}