Surely we can assume there was a lot of Raffaele's and Amanda's DNA in the room that was "rubbed off", disappeared, went unnoticed, whatever. The problem is we need to find a plausible scenario, not just a scenario. All the other elements already make Amanda's and Raffaele's involvement implausible: the time of death, the lack of motive, the impossible kitchen knife story, Guede's background, etc.
If you absolutely need to postulate something very implausible to support what is already defying belief, where is the moment that you stop and think: maybe just maybe it doesn't make sense after all?
Who thinks he was scrubbing? Rinsing blood will not deposit one's DNA like a forceful struggle will.
To me it's absolutely clear that Guede deposited Meredith's DNA in the bathroom because the blood he was rinsing was Meredith's. Also, there were many more samples taken in the bedroom than in the bathroom.
There was no fight, no struggle, no murder, no ripping clothes apart in the bathroom.