I have 3 tanks at the moment,
Tank 1 - bloody mary shrim with neon and ember tetras, though 90% of the shrimp are wild type now!
Tank 2 - the old taiwan bee shrimp tank, has 11 mosquito rasbora and 1 killie with wild type cherry shrimp, I have just done the maintenance on that tank and there are definitely shrimp still doing well (I don't feed shrimp in there) but they are clear or brown so VERY difficult to spot! I tested this tank last week and parameters were ideal for taiwan bee (PH6, TDS 140, KH 0-1, GH 5-6 (a bit high)) as it has been since set up.
Tank 3 - male betta with wild cherry shrimp, again just done that tank and there are shrimp doing well in there but again, I can ony see them with a strong light and magnifying glass due to their lack of colour.
I am looking at maybe just stocking up before winter so may get a job lot of bloody mary shrimp for tank 1 (and discard lots of wilds) and have a final try with the taiwan bee as the tank 2 is at the moment. The parameters are perfect but the plants are still not nice and green with this substrate, as they were before with the other substrate but obviously shrimp are living in there, albeit not ones I wanted, so I can rule out disease and poisoning. As you say, the taiwan bee are much easier to see so may be preyed on by the fish so I won't buy expensive ones (ebay probably) or a large quantity (if I get any at all of course, though it is now or wait until next year). It would be the last lot I try until the fish die off and the tank is reset with the other substrate!
Simon