Last train from Osaka to Hiroshima

Our flight into Kansai Airport has been changed to arrive at 7.25pm.
It is an international flight, so we will have to clear customs and retrieve our bags. Assuming all goes well and we are out by 8.30, is it possible to get to Hiroshima that night. I entered an 8.30pm start time from Kansai Airport in Hyperdia and I think the result is, we miss the last train from Shin-Osaka to Hiroshima and would have to stay in Osaka. Is this correct?

If you will be using a nationwide JR Pass and you can't take the Nozomi, then yes, too late for the last connection.

I guess you searched on Hyperdia with "Nozomi/Mizuho" button unchecked. If you check this button (default), there are some Nozomi shown.

http://goo.gl/ilsjD2

If you are JR Pass users, you can't ride Nozomi for free, but if you pay full Nozomi fare (fare and seat fee) of course you can use it and reach Hiroshima on the same day.

It depends on your entire itinerary, but you may want to consider Kansai Hiroshima Area Pass

http://www.westjr.co.jp/global/en/ticket/pass/kansai_hiroshima/

with which you can take Nozomi for free (non-reserved seat only).