I've done both and haven't had any problems of the discus messing with them. Actually, it's the other way around, watching the little guys bowing up to the discus 10x their size to get food is hilarious. But my tank has decor and substrate. However, apistos tend to do better in 78-80F (26-27C) temps, but rams shouldn't be a problem. Just make sure you buy rams from a good source. Most rams being sold in the US have crappy genes and aren't well cared for by the importers and thus die within a month or two of you having them.