It all depends on the frequency content and the length of the coax.
With the design as you have shown it, the 50ohm coax is improperly terminated, and this
will manifest itself as a ripple in the amplitude vs frequency response of your probe+scope. Professional scope probes avoid that by replacing the "good" transmission line with a very lossy transmission line of very special coax (>100ohms/metre DC resistance, centre conductor not being straight, etc). To see those effects, you can quickly model the system using a lossless transmission element. Fundamentally, it is difficult to make a good homebrew high impedance passive probe.
An alternative, since you have a low impedance source, you
can easily homebrew a "low impedance Z0" passive probe - and these have remarkably good frequency response; 40 year old professional probes had 1.5GHz bandwidth, and modern ones have 6GHz bandwidth.
FFI, have a look at the references at
https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/