It is a correct Budd dome.
Nope, Lionel's dome is not even correct to represent the dome pictured, which is an ex-D&RGW car. The Rio Grande car has curved glass on the lower windows and Lionel's has flat glass. Also notice the D&RGW's dome windows are angled forward slightly.
The two cars shown above are Budd domes but they are not a common style of Budd dome. These were built for the C&O's Chessie train and had low domes so they could operate through tunnels particularly the one leading into DC Union Station. To my knowledge there were only six of these type domes made - 3 dome/coach/observations and 3 dome/drawing room/cabin cars all for The Chessie. When that train was cancelled the observations went to the Pere Marquette district of the C&O for a few years before sold to the D&RGW. The straight domes went to the B&O. These are unique cars and have only been made in HO brass.