No, Umbridge did not witness any negative interactions between Snape and Neville. Also, her focus was on monitoring what the students were taught and removing Dumbledore’s close allies, not treatment of students.
When Umbridge inspects Snape’s class, Snape does not interact with Neville specifically, in either a positive or negative way. He does express his displeasure with Harry, but Umbridge is questioning another student at that time, and it’s unclear whether she noticed.
“She turned away, walked over to Pansy Parkinson and began questioning her about the lessons. Snape looked round at Harry and their eyes met for a second. Harry hastily dropped his gaze to his potion, which was now congealing foully and giving off a strong smell of burned rubber.
‘No marks again, then, Potter,’ said Snape maliciously, emptying Harry’s cauldron with a wave of his wand. ‘You will write me an essay on the correct composition of this potion, indicating how and why you went wrong, to be handed in next lesson, do you understand?”
- Harry Potter and the Order of the Phoenix, Chapter 17 (Educational Decree Number Twenty-Four)
However, even if she did, it’s unlikely she would have cared. Umbridge was not at all focused on how the students at Hogwarts were treated in class - her mission as a Ministry employee was to ensure that students were not being taught anything that they could use against the Ministry. The reason she was placed in Hogwarts to begin with was because Fudge thought Dumbledore was training the students to fight in an army against the Ministry.
“Ah, well, that figures,’ said Sirius. ‘Our information from inside the Ministry is that Fudge
doesn’t want you trained in combat.’
‘Trained in combat!’ repeated Harry incredulously. ‘What does he think we’re doing here, forming some sort of wizard army?’
‘That’s exactly what he thinks you’re doing,’ said Sirius, ‘or, rather, that’s exactly what he’s afraid Dumbledore’s doing – forming his own private army, with which he will be able to take on the Ministry of Magic.”
- Harry Potter and the Order of the Phoenix, Chapter 14 (Percy and Padfoot)
Umbridge also was likely trying to get rid of any teachers she considered too close to Dumbledore, so he would have less allies against the Ministry.
“Hagrid … please …’ said Hermione, a note of real desperation in her voice. ‘Umbridge is looking for any excuse to get rid of teachers she thinks are too close to Dumbledore. Please, Hagrid, teach us something dull that’s bound to come up in our O.W.L.”
- Harry Potter and the Order of the Phoenix, Chapter 20 (Hagrid’s Tale)
Umbridge’s goal was to make sure Dumbledore could not successfully raise an army against the Ministry. How any teacher behaves towards any particular student would not be her concern, without any larger reason why she should care. When she inspected Snape’s class, she questioned him about his background and told him the Ministry would not want him teaching the students how to brew a Strengthening Solution.
“Right,’ said Harry vaguely, putting down the bottle and continuing to watch the corner. Umbridge had just got to her feet. ‘Ha,’ he said softly, as she strode between two lines of desks towards Snape, who was bending over Dean Thomas’s cauldron.
‘Well, the class seem fairly advanced for their level,’ she said briskly to Snape’s back. ‘Though I would question whether it is advisable to teach them a potion like the Strengthening Solution. I think the Ministry would prefer it if that was removed from the syllabus.”
- Harry Potter and the Order of the Phoenix, Chapter 17 ()
Umbridge does not evaluate how any of the teachers at Hogwarts treat their students. Additionally, she heard favorable comments on Snape, so would not have been particularly inclined to remove him.
“You are on probation!’ shrieked Professor Umbridge, and Snape looked back at her, his eyebrows slightly raised. ‘You are being deliberately unhelpful! I expected better, Lucius Malfoy always speaks most highly of you! Now get out of my office!”
- Harry Potter and the Order of the Phoenix, Chapter 32 (Out of the Fire)