How does your new version of dungen_render_tile look? New-style tiles changed from coordinates to a 0-N index so if you pipe in the same coordinates as before it would probably create tiles outside the range of the tileset. Also, the example tileset is organized in a special way and this is used by _render_tile (first row has 6 floor tiles, second row has 6 wall tiles, third has 6 obstacle tiles, so it picks an x coordinate between 0 and 5*TILESIZE and an y coordinate based on the tile type), if your tileset is arranged in a different way you'd need to adjust how the coordinates are picked to suit this. Okay I didn't see your first message, seems like you already tested the tileset arrangement issue.
As an intermediate debug step, try creating objects rather than tiles (with instance_create_depth) and make bright-colored squares for the placeholder walls and floors, this should at least tell you if the spawning is done correctly. (I would wager it's done correctly if the doors show up in the right spots, but it's best to make absolute sure).
If you still don't see anything when spawning placeholder objecst, you could try adding a show_debug_message() to their create event where they print their x/y coordinates (if those messages show up, but you can't see the objects, just compare with the player's spawn point to figure out where they spawn; if the messages aren't printed, the objects aren't spawned at all)
