No, you don't NEED to use an undergravel filter at all. There are other options, all have their pro's and con's. Simple sponge filter with a powerhead works well, see my signature "Cheap filter". UGF's are preferred by some since they are not as visible. But they are harder to clean.
I wonder why plastic plants though... even if it isn't going to be a lush CO2 injected masterpiece, adding a bit of sand and sticking some plants in there can only be good for fish (and people)?