Hmm, that's a lot of fish for a 30 gallon high, the pleco alone needs a larger aquarium (like 55 gallons). Have you tested your water for Nitrates, Nitrite, and Ammonia?
Rosie Reds aren't a good food source and could contain parasites and disease though.
I'm not sure why clawed frogs some times ignore certain fish. It's possible the frog does make attempts on these fish at night or when you're not around though or the fish just are too large for the frog to eat. Most predators like clawed frogs prefer to take prey 1/3 their size, the fish may just be big enough to seem to large for the frog to eat. Your frog appears to be male, males are a lot smaller smaller than females. A female frog probably would have cleaned house by now..
Right. They will escape from holes in lids or open tanks. I myself use a glass lid and I use two clips to keep the glass lid propped open just 1/4th of an inch to allow air in. I lower my water about 3 inches from the top to allow an area to breath safely. The back is plastic and cut to fit my canister filter tubes, it's not an exact fit, so some air can get in that way too.
Don't worry too much about what type of filter you use. I've used all kinds of filters with my frogs. I use a canister filter these days though and do not regret it. They offer the best filtration in my opinion and they are very quiet. Also make sure you are keeping up on partial water changes. I change out roughly 30% of my 40 gallon tank per week, it houses 4 clawed frogs (3 large females).
As far as food is concerned, try canadian nightcrawlers. I buy mine at Walmart in the fishing area, they are just bait worms and they work very well. I feed my frogs 2 nightcrawlers per week, some times I feed my frogs reptomin, which is also fine for frogs too. You can throw in some other stuff for variety, like frozen foods, clawed frogs will eat anything.
I use water sprite/indian fern for a floating plant, it provides cover and makes the frogs feel safer. If you can find some in your area I would recommend it, it grows very fast and will quickly cover your aquarium. I throw mine out by the handful because it is basically an aquatic weed.