According to GM, those are taboo:
Thats interesting, never seen that service bulletin before. Though after reading it I think it's highly subjective and likely masking other issues GM has had.
Common sense comes into play with any form of abrasive use.
They mention that it can take "about 15 seconds to remove 0.203 mm (0.008 in) of metal with an abrasive pad". Who in their right mind holds an abrasive disc at 10k rpm in one spot? Nobody. When will they claim that it is not advised to use a DA on the paint since you can easily damage paint if held in one position for more than 15 seconds with a highly abrasive compound and pad?? If you use light pressure, use a fine grade and keep moving you'll have zero issues.
They go onto to mention "The presence of Aluminum Oxide in engine oil has been shown to cause premature engine bearing failure. In some cases, this failure occurs in as little as 2,200 km (1,367 mi) or less after the repair has been made." It really begs to question the amount of aluminum oxide concentration that takes. It also comes back to common sense. Are people not cleaning the part re-sealing before installation?? Abrasive dust is very noticeable when using the Scotch-Brite pad style discs, you can see it in the air and with how quickly the pad degrades. With the Bristle discs you can do 20-30 jobs with one disc and the only noticeable amount of debris is the material you are cleaning. You should always remove the large chunks of old sealing compound before surface conditioning also.
There should be zero fear using bristle discs. Just don't use the Yellow or Green for aluminum and you'll be just fine. The 3M bristle discs are used widely in the automotive industry, especially the White/Fine Grade. It's not impossible to remove excess aluminum, but it takes an obvious amount of effort! Bristles start flying and you have to use enough pressure that it slows the air tool almost to a halt. There is no question that the abrasive pads take more finesse, create a lot more dust and wear out extremely fast. I have worked on hundreds of cars (as a technician) using the White bristle discs. It takes a long time for those to wear down, which indicates that there is very little possibility of contaminating the engine in any form. Otherwise I would have seen cars come back with blown engines from all the "aluminum oxide" they supposedly spew into the engine over the last 10+ years I've been using them.
In fact it can be argued that the very slight (you can't feel it with your finger nail at all) amount of cross-hatching that the bristle disc adds to the surface aids in sealing, just like a head that has been freshly machined. You don't want a mirror finish polish! If there is nothing for a sealing compound to adhere to, it will essentially just squirt out and you'll be back to square one in a short amount of time.