Glows and flares are a post render effect, so there is little harm in using the Maya software renderer to composite passes together, as is the normal workflow.

It's not that these effects don't work in mental ray - they do. If you, say, increase your intensities x10 and use mental ray the effects will appear. The main thing you will notice is that the effects are not as smooth as they appear with the software renderer.

As far as glows (specifically) are concerned, you could fake them with a samplerInfo / facing ratio node driving transparency. As you can see, I have two spheres. The inner sphere has incandescence applied (see Attribute Editor), the outer sphere has the "fake glow" network at the bottom of the Hypershade applied.

Sorry, can't give you lens flare...yet.