I went to Alton Towers last year. Really enjoyed it but yes, if I'd been stuck on a ride for 2 hours, that could've become hairy.
I took glucose tablets with me (which I'd highly recommend) so I should have been ok if there had been a stopped ride. I didn't have my testing kit so would've had to watch for hypo symptoms, which could be harder in an anxious situation.
However, this is hypothetical as my day went without any hitches.
There's quite a bit of walking between rides so that needs to be taken into account. I tested before each of the bigger/longer rides.
The night after, I think I had lower sugar levels than normal, which was probably down to the extra walking but also could be an after effect of having had several adrenaline rushes
So my advice would be to treat the day as you would for a day that involves a fair bit of exercise and definitely take glucose tablets with you. The GlucoTabs come in a plastic tube so are well suited for the rides involving water.