Yeah, you get in-bounds access to the allocation so sub-allocation attacks/cross field is in the play. It's kinda a pain in the ass to turn that into a useful exploit primitive though, and anyways UAF is much easier because (at least with classic allocators) you can corrupt any allocation type. Hardened allocators make exploitable overlaps much harder though and so in practice CHERI's spatial safety might be enough to kill tons of bugs.