Hi,
As far as i aware : ISP'S are using MPLS in order to provide easy i& connecitivy for their clients.
MPLS (Multiprotocol Label Switching)
As long as this MPLS is enableing your site to connect back to the controller (and MPLS dosent blocking IPSEC by default)
so there is no problem at all as far as i see it.
have a gr8 day.
me