Draft JVMS 3ed specifies the requirements on array type descriptors in 4.3.2
section:
  ---Excerpt-from-spec---
  A type descriptor representing an array type is valid only if it represents a
  type with *255 or fewer dimensions*.
  ---End-of-excerpt---

JVMS section 4.4.6 states as follows:
  ---Excerpt-from-spec---
  CONSTANT_NameAndType_info {
    u1 tag;
    u2 name_index;
    u2 descriptor_index;
  }
  ...
  The items of the CONSTANT_NameAndType_info structure are as follows:
  ...
  descriptor_index

  The value of the descriptor_index item must be a valid index into the
  constant_pool table. The constant_pool entry at that index must be a
  CONSTANT_Utf8_info (4.4.7) structure representing a *valid* field descriptor
  (4.3.2) or method descriptor (4.3.3).
  ---End-of-excerpt---

However, JVM class format checker does not reject classes with invalid (more
than 255 dimensions) array type descriptors at the descriptor_index in the 
CONSTANT_NameAndType_info structure.