In my opinion the answer would be yes. I believe a grant proposal development to be of similarity to a business case. These items are deliverables of some need and could be a project in and of themselves. You just need to make sure that you can document and prove that these items followed all or some of the processes outlined in the PMBOK and that these items were a result of an actual project by definition.
I have developed many business cases which were considered projects, in order to get a trigger for another project, whether or not the business case was accepted or not. I set it up as close to the PMBOK as I could in these cases.

Thanks for your response! To be sure how to proceed, I would appreciate feedback considering the additional details below:

I'm wondering if the process of developing and finalizing a grant proposal and its supplementary plans/docs would be considered part of the project initiation phase. Or, is it considered pre-project work. And if it's pre-project work, can it still count towards the hours required by PMI for PMP certification? Developing a grant can require a ton of man hours as it includes needs assessments, feasibility studies, stakeholder analyses, risk assessments, objectives, a timetable, etccc. Moreover, this process is done iteratively with a lot of back and forth between the donor and the implementing organization, until both parties are satisfied. Once final and approved, the grant proposal becomes part of the grant contract. Basically, I see similarities between the process of developing a grant proposal and the process of developing a project's business documents. So, does this work count towards PMI's required hours? If yes, should it be described as part of the Initiation Phase? Note that including this pre-contract work means changing the start date of the project to before the contract is signed. I have my supervisor's support, but how/should I explain this in the application?
Thanks for your consideration!
Stephanie

All projects have a definite start and finish. The project start usually is documented with a charter of some form. Contracts could be triggers for the project at the start and could be the start date. Now in your case, you may need to have on hand some documentation that proves a start. This of course would need your Supervior's concurrence.

Hello all! I have a lot of Project Management experience leading grants for a non-profit in the West Bank. I am a bit confused filling out the PMI PMP application because I'm not sure what to list as the project start date. There is so much work involved in developing and refining the project proposal/plan alongside the donor (sponsor), that I'm sure this should be likened to the Initiation Phase. However, this work happens before the contract is signed and the project is officially begun. My question is, can I list a start date earlier than the signing of the contract in order to account for the Project Initiation Phase? Thanks in advance!

Also, if anyone has knowledge in nonprofit project management and would like to discuss applying PMP terminology to that field, I'd be happy to join that discussion.