The spell checker engine is not designed to share dictionaries across a network. However, it may be desirable to share a custom dictionary between users. The only way this can be done reliably, is to store the dictionary as a list in a shared datafile. The spell checker allows you to do this by opening one or more memory only dictionaries, see SPLLopenUserLex.You can open a memory only dictionary, by not specifying a dictionary name. You would specify the list of words from your datafile in the second parameter.
You will need to make some changes to the window wSpell when a user adds a word to the memory dictionary. As well as adding it to the memory dictionary, you will also want to add it to your list and write it back to your datafile.