By default, they woud not import their own routes back in. Because the CE's would see their own AS number (loop prevention).
If allowas-in is used on the CPE's, then the engineer would just need to understand what they are doing. I do not see a benefit or a goal for purposefully accepting already known routes. Not optimal, but not a huge issue.
NOTE: my experience with Juniper, is that by default the PE will not advertise the AS to the same AS. Needs an extra config line to make that happen.
I do not see AS numbers on this BGP map. The way it is drawn, I am guessing that it is the same provider, and the CPE's are using same AS# . Is this correct?