Okay so Season 1 ends with RF being erased from reality.
Season 2 gives us an RF that has NOT yet gone back and killed Barry's mom. The explanation is that by time traveling within the speed force, RF was unaffected by the temporal erasure and that he is a remnant or perhaps a living/breathing time paradox.
This is not the first time that sci fi has shown that time travelers are immune to changes in the timestream while they are traveling.
1. Back to the Future 2: Marty and Doc return and find they are in the alternate 1985 and find out how things are twisted and what happened to their alternate versions. We also see that time changes cause a ripple affect that carries forward in time such as the newspapers changing and the fax of Marty being fired erases and of course the polaroid in the first movie.
2. 90's Xmen cartoon: Bishop goes back to save Senator Kelly, he goes home and we see that Forge knows nothing of the original mission given that his memories altered with the timeline and that a plague is running amok. When Bishop returns again after stopping the plague, Forge knows nothing of it as his memories have again altered with the timeline while Bishop is unaffected given that he was outside of time.
so yes, RF could be exempt from the erasure by time traveling and being in the speed force. My main sticking point is that as soon as he emerged in Season 2, that the erasure effect should have caught up with him and erased him, however he is a time paradox so the erasure may not affect him. Also the things he did in the past have happened and thus must happen as this RF must go back and do them before being erased.
Temporal Mechanics: you gotta hate it sometimes.