De Vries has been a reserve driver all season and has been following race weekends in the Mercedes garage. He took part in an FP1 session for the team when he stood in for Lewis Hamilton in France.
In Singapore, as it became clear that he was likely to land an AlphaTauri driver next season, he was obliged to take a step back.
He was no longer involved in all meetings through the weekend as the flow of technical information closed down, and that arrangement continued in Japan.
However, the team still has to deploy a rookie FP1 session, and de Vries is expected to drive George Russell's car on Friday in Mexico.
Elliott says the team has no concerns about de Vries getting a taste of the team's latest developments before heading to a rival camp.
"We're really pleased for him, for the opportunity he's got," said Elliott. "Maybe a shame where he's going, but that's what it is.
"I think he deserves the opportunity, I think he's shown he's a very good driver. Having him in the garage has been brilliant, he's a really nice guy, very switched on, and he understands the car.
"I think we have faith in him that we can put him in the car, we can do tests with him, and we can trust him to not be looking at the things we don't want him to look at, and I think he'll do a good job."
Elliott noted that de Vries has done relatively little sim running, as he's been focused on his own racing programme: "He's done some. Obviously, he's been driving Formula E as well, which takes up a big chunk of his time.
"But again, F1 changes so fast. That learning comes at such a pace that what he's done a year ago isn't probably particularly helpful to him. I think more what he might take away from here is the way we work together, our processes and our systems.
"As I said, I guess what we want is to wish him luck. I think he's been very honourable in the way he's dealt with us, so no concerns."
De Vries stressed that, unlike Russell, he wasn't a Mercedes protege, and was thus always free to go elsewhere.
"I guess I was perceived as a Mercedes driver in the past couple of years, which I was to an extent that I was racing for them in Formula E, and active as an F1 reserve driver," said the 27-year-old.
"But apart from those contracts there was no other affiliation. Of course, we built up a very friendly relationship over the year. So they've been very supportive and helpful.
"But at the same time, I'm here to look after my own interest. Of course, I hope that they are disappointed to lose something. I don't know! You may [have to] ask that question to them.
"But I also think that they are pleased for me and happy to see me getting an opportunity on the grid in F1 next year."
