How do they perform for film scanning? I had read you have to use them backwards for best results.
I use a EL-Nikkor 50mm f/2.8 reversed with a small extension tube, it’s almost 1:1. Quality is good corner to corner even with balsam separation on my lens.
Focus is very critical so you have to use a macro rail.
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You can use an enlarging lens but it should indeed be reverse mounted for best results. An enlarger lens is better than a standard camera lens for film scanning. A good macro lens is better than an enlarger lens. A scanner lens is better than all of them. Period.
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I’m using a Schneider Componon-S, 80mm f4 coupled to an Olympus Auto Bellows, with outstanding success. This is all mounted on a Sony A7riii and the lens is not reversed.
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You can read extensive tests of many kinds, models and makes of lenses, including enlarging lenses, at https://www.closeuphotography.com/ and https://coinimaging.com/. Generally, enlarging lenses are not optimized for 1:1, or 1:1.5 for smaller chip cameras, and don’t do as well as lenses optimized for duping. These experts do have applications for enlarging lenses at higher magnifications, but not for most of us digitizing film at 1:1.
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It depends on how you define outstanding success 
I guess that I should probably defer to your definition, since you appear to have a much more defining interpretation of the term.
True, success is subjective.
With respect, for better results, the Componon-S 80mm F4 should really be reverse mounted. If you think about it, camera scanning is the reverse of darkroom enlarging and the rules of physics/optics will always prevail.
Reversing an enlarging lens for 1:1 duping makes no difference that I have ever observed in my own experience or read about by anyone, but I’d be happy to stand corrected with links to well-conducted tests. Caveat: most enlarging lenses of this type (Componon-S 80mm f/4) are symmetrical design, often six element, and optimized for somewhere between 8:1 to 12:1. So if you reverse mount it, you still have the same non-optimized problem. There are advantages to reverse mounting when going to higher magnifications. On the hopeful side, if you are using the 80mm lens for 1:1 duping of 35mm film, your lens extension is such that you are using the better-performing center portion of the lens with a very large image circle.
I was a little slack in my comment - it only applies to asymmetrical lenses.
I’ve tested a dozen macro bellows-mounted enlarger lenses with a Canon 6D. Getting satisfactory quality in the center is within reach of most, but there are big differences in homogeneity. The best results come from the APO-Rodagon N 50mm, and the El-Nikkor 80mm and 63mm. The results are better than what I get with the Sigma 50mm DG Macro, but I haven’t tested any other macro lenses. The Nikon 50mm is not bad, but a step behind these three.
I’ve compiled the results in this thread on another forum (in French): Comparatif d'objectifs d'agrandisseur pour numérisation avec APN - Forum photo argentique
The results would surely be different with another sensor, and would perhaps make it possible to differentiate the best.
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Excuse me asking after such a long time but I was wondering how you mounted an enlarger lens to the Olympus Auto Bellows, it doesn’t look easy. I have succeeded because I happen to have an adapter that someone made utilising a 49mm filter with the glass removed with a 39mm female threaded insert glued in place (I don’t know where that came from), this mounts directly to a secondhand 49mm OM reversing adapter. If I didn’t have that I could also have gone with a 49mm male to M39 female adapter joined to the reversing adapter with a male to male 49mm connector. You can find these adapters on-line but they’re not common.
Pretty sure you could also use an OM T-mount adapter in a similar way, Rambex make a T-mount or M42 male to M39 female adapter. I haven’t found anyone that makes a straight M39 to OM body adapter, not sure anyone ever did, Olympus catered for their own lenses rather than enlarger lenses I think. Reversing and T-mount adapters have to be bought ‘used’ I think.
It also works with macro bellows with other mounts; I use one with an M42. But it’s true that the Olympus is of very high quality and it may be worth finding a setup.
Yes, Canon actually made their own ‘FL/FD’ lens adapters to go to both M42 and L39 (P & A Mount Adapters respectively). I’m not sure if Nikon did at the time but now you can get nicely made metal ‘flange’ adapters to go to either M42 or L39. Strangely nobody seems to be bothering to make adapters like that for Olympus OM. Just like the better Nikon bellows the Olympus slide duplicator extends beyond the bellows and is adjustable, so pretty useful. I’ve read that the Nylon blocks in the bellows can deteriorate with age though.