As I understand it DNA and RNA store their information in the form of certain amino acids. If other life uses amino acids in a similar fashion they may not use the same ones that life on Earth uses. Life here uses I believe 20 different amino acids and there are several hundred known.

So there's potential there I would imagine in regards to testing that hypothesis. However what mainly bothers me with it is that it doesn't explain the origin of life and why Earth couldn't have original life begin on it.

Unless we can rule out that early Earth conditions would have been too inhospitable for life to start but was sufficient to sustain it I see no reason to think an extraterrestrial origin to Earth life is more likely.