While I can see some benefits, when it comes to conjurer the cons outweigh the pros. We lose Regen, Divine Seal, and Benediction. Regen saves a ton of MP, Divine Seal can greatly boost our curative skills and Benediction... well, that needs no introduction.

Cross-class skills are hugely limited for Conjurer and the ones which can truly benefit us are also available to us as White Mage. Furthermore, the soulstone not only gives us access to those skills, but also increases our stats.

So, yeah... it can be done. But that doesn't necessarily mean it should be done.