Caddy and B-Line both make brackets that are designed to clip onto the grid and support a box anywhere in the tile. The 'customary' wiring method is for the last part of the conduit run to transition to flex or MC; then you can still move things if needed.
Yet, these days we're not supposed to 'support' anything from the grid. Light fixtures need their own support wires. Would this bracket also need to have wire supports too? Or, is the support of the conduit enough?
What if the ceiling tile has been replaced by a wood panel, and the box attached to it?
I fear we have pretty much made the suspended ceiling obsolete.
Reno, 314.23(D)(1) does make it sound like those caddy clips are legal if the box is smaller than 100 cu/in
(D) Suspended Ceilings. An enclosure mounted to structural or supporting elements of a suspended ceiling shall be not more than 1650 cm3 (100 in.3) in size and shall be securely fastened in place in accordance with either (D)(1) or (D)(2). (1) Framing Members. An enclosure shall be fastened to the framing members by mechanical means such as bolts, screws, or rivets, or by the use of clips or other securing means identified for use with the type of ceiling framing member(s) and enclosure(s) employed. The framing members shall be adequately supported and securely fastened to each other and to the building structure.
I still imagine most AHJs will want to see a supplemental support wire or two. You could do the EMT thing if it was supported by the building structure within 18" of the box. I have seen smokes and alarm beacons or beepers in a 1900 box, hanging in the grid but they were on an MC whip.