I personally don't reccOmend it, but I know a few folks have osmicote with no apparent I'll effects. The pellets were placed in the moss surrounding orchid roots and stuffed into cracks in a cork bark background
I once a fert similar to Osmocote in a fish tank and one of the species of fish ate a few of the pellets that got loose from the gravel. I think they saw them as eggs. Every one of those fish died.
Osmocote is a lot of fert too. It's probably more than most viv plants need unless you are growing them under real bright light. The more humid conditions are the faster the ferts will release through the plastic Osmocote membrane.
The more you feed your vivarium's inhabitants, the more natural fertilizer they'll produce... I've used fertilizer before, and I don't notice too much of a difference between that and just letting the frogs poop do the trick. Frog poop is free and you don't have to use your time to put it in there.
I'd recommend waiting to see if you actually NEED fertilizer. Many smaller tanks don't, and orchids bloom fine with no additional help. If you see deficiencies then I'd try some sort of fertilizer, but a mild one. A little bit of worm castings worked around the orchid's mount may be better than the pellets. Mineralized soil is also popular in fish circles for heavy root feeders, and is safe for delicate shrimp (which is a really strict test! doesn't take much to kill them!).
The only tanks I've seen that NEEDED to be fertilized usually either didn't have frogs in them, or had VERY low densities with low food densities as well (reliant on microfauna as well as additional feeding).
I often remove sludge from the pond (broken down leaves, waste, etc) with a spoon or turkey baster and squirt/spoon it around the base of plants in the tank.