Hi Tim,
Is SSLCIPHER a client or server SSL profile? A virtual server in a specific (non-Common) partition can reference objects (including a client or server SSL profile or iRule) in the common partition. A virtual server in the Common partition would not be able to reference an object in a specific partition. This is detailed better in the Config Guide:
Configuring Administrative Partitions
https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/tmos_management_guide_10_0_0/tmos_partitions.html
The other case in which one object can reference another is when the object resides in one partition, while the object it references resides in partition Common. Figure 5.3, shows an example of this configuration, where a virtual server in partition my_app references a pool in partition Common.
[...] the referencing object (the virtual server) must be in a user-created partition (my_app), while the referenced object (the pool) must reside in partition Common. As shown in Figure 5.4, the virtual server cannot reside in partition Common and reference a pool that resides in partition my_app.
I don't think there is much restriction around iRules though. You can reference any valid object which exists in any partition from an iRule regardless of which partition the iRule is defined in.
Aaron