Is a bioluminescent analog to hemoglobin possible?

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You might consider adding luminol to the creatures' bloodstreams. When mixed with an oxidizer (like oxygen) and a catalyst, it becomes luminescent. It turns out that the iron in hemoglobin is a very good catalyst, which is why it's sometimes used at crime scenes to track blood.

The glow dies away quickly, within a minute, meaning that it would have to be constantly replenished. Luminol is not organic, so the organisms couldn't simply produce it. Perhaps it's found easily in the soil or ground on the planet, or maybe it doesn't mix with the blood or an oxidizer until the creature dies. Now, justifying its presence is a bit harder, given that it's not organic. Evolutionarily, it seems to serve no purpose. Again, maybe it just happens to be present in the surrounding environment. The organisms certainly wouldn't need it to survive.

As Joe Bloggs pointed out, the oxygen should be stored in the hemoglobin, which implies that it shouldn't react with the luminol. I don't know if the reactions between the iron in the hemoglobin and the luminol could free up some oxygen; if not, then there won't be a reaction until the luminol (and thus the blood) is exposed to air - just like in the situation described, when the organism dies.

The result of luminol's chemiluminescence? A blue glow:

^{Image courtesy of Wikipedia user The Viewer (David Muelheims) under the Creative Commons Attribution-Share Alike 2.5 Generic license.}