Is getting up many times during the night to urinate a symptom of vascular dementia or could it be something else?

I'd get medical appointment for a checkup. I presume the Doctor would want to rule out infection/disease/medication reasons first - before concluding it is a neuological reason?

Eg urine sample for UTI strains, bladder & kidney function, medications with side effects?

Incontinence is a known effect of brain changes of those with dementia. But if it is something else, something with a cure, of course it is better for all to aim for that.
If cure is not possible, then contain: the right incontinence briefs + bed protection + something to help sleep better/longer?

My late husband(who had vascular dementia)had the same issue, however he got up every hour on the hour to pee. And yes, if you Google symptoms of vascular dementia, incontinence is one of the first ones listed, and my husbands urologist and neurologist both equated it to his dementia.
It's exhausting, I know, as I had to get up with him as he was a fall risk. So neither one of us were getting any sleep.
We tried pretty much all the bladder spasm medications and none worked. His urologist also put Botox in his bladder as that is supposed to help calm the bladder down, but that too didn't help.
I would even get up and hold the plastic urinal for him so he wouldn't have to get up so much. And of course by this time he was wearing Depends as well.
After about 8 months of no sleep(which about killed me)his urologist finally recommended that my husband have a supra pubic(permanent)catheter put in, and FINALLY we were both able to sleep through the night. And I only had to empty his catheter bag twice a day. It was a Godsend for sure.
So talk to your husbands urologist and see what he recommends.
I wish you both the very best as I know how very hard this is.

This can be a symptom of so many things. Therefore it needs to be reported to the MD. If there is a lot of sodium intake in a day nighttime visits to the bathroom may be more frequent. Also there is evidence that people who have some vascular insufficiency for whatever reason have fluid move up from the periphery with elevations of the legs, making it easier for the kidneys to eliminate excess fluid, making more frequent nighttime visits.

Some increase of trips to BR is normal. But it is still reportable to the MD.

He may have an enlarged prostate. They get the urge but have a hardtime going. Funny, though he doesn't have the problem during the day.

I would take him to a urologist. It could be one of several things at his age. Not getting sleep and also disturbing yours is worth looking into. He may not be completely emptying his bladder when he goes. He may not be able to. That’s not to say the dementia is not affecting his habits but not everything that goes wrong with an 88 yr old is caused by dementia.