Different tops should make no difference.
The problem with Ritek is that their quality is too variable. Not all batches of "grade A" Ritek are the same. Some are good. Some suck.
I guess what Ssseth is saying is that the shiny "grade A" RiData discs tend to vary unfavorably compared to the silver mattes. I have no evidence to support this either way, though.
Sharpies should be fine. There is a LOT of plastic between the top and the recording layer for DVDs--much more so than for CDs, so you should be fine.
Though if I were you, I wouldn't get Riteks (as a person who's gotten two RiData batches before, I think they're overrated... though I guess considering their price, they are probably still worth it)