Is the terminal emulator set up correctly in regards to baudrate and stopbits? I would try playing around with these settings. Maybe even go as far as to RTFM.

I haven’t used Dell gear before, but you are sure that it’s not some proprietary protocol that’s running over serial? As in it requires some special software instead of a console?

I’m not sure what you mean by the signals being dirty. If it’s the slope after the initial fast rise you mean, I guess it could be remedied with an opamp, a push-pull pair, an optocoupler, or some other switching circuit with a suitable power capacity. But as long as it gets above the hysteresis threshold for long enough it should be fine. Whether that’s happens you should be able to tell from the scope (which I can’t see while writing in my client)