Online Travel Booking and Bidding Agencies - Question on Expedia Itinerary

I'm looking at booking a trip from DEN to YWG and the cheapest routing I can find is as follows:

DEN-ATL-ORD-YWG

The DEN-ATL portion is operated by frontier airlines (rest is UA), is this similar to being on a code share flight? IE would baggage be checked through to my final destination? If I missed my connection from ATL-ORD, would UA be responsible for getting me on another flight?

If it is all on one ticket then interline bag handling is no problem and they are supposed to deal with you missing a flight the same as if you came in on United... That being said - how good are they going to be to someone who misses a flight irrespective of who delivered them to the connection late is anyones guess! If the bags do not arrive at your final destination it is the carrier who delivered you to that point who is responsible for finding and delivering the bags to you...

Thanks, I ended up purchasing it and its all ticketed through United. I called them up and they said the connection in Atlanta from Frontier to UA is guaranteed. I have almost 2 hours at both of my connections so I hope it will all work out.