I'm not sure, but I think it depends on the bridge.
I have two Teles built up here. One has a hollow body using a Maple cap over a Swamp Ash carcass and a Kingwood over Canary neck with a Graphtech nut and locking Schallers. I used the Gotoh humbucker Tele bridge on it with Graphtech saddles.
The one in this thread is a hollow body using a Mahogany cap over a Mahogany carcass and an Aframosia over Aframosia neck with a Graphtech nut and locking Schallers. I used the Scartozi bridge on that with Graphtech saddles.
You would think the first one would be painfully bright, and the second fairly so, but that's not how it worked out. The one with the Scartozi bridge is dramatically brighter, with much greater sustain. I mean, when you pick it up and strum a chord, your first question is WTF? It just rings like a bell. You don't have to listen for it, It jumps right out at you.
So, tone loss? I don't think so. At least, not because of the saddles, if at all. Not that the first one is suffering from lack of tone - far from it. It's been just about the only thing I've been playing because it sounds so good. But, compared to this new one, the first one is dead.
As close as I can tell, the only downside to Graphtech saddles is the cost. They want ~$40 a set for the little buggers. But, they do a good job, so what the hell? It's a pretty small percentage of the overall cost of the instrument and I think they return better articulation and sustain than most OEM parts.