Exclusivity applies to home office deductions. According to the IRS, an expense must be necessary and ordinary to be a business expense write-off.
Yes, if you use the membership for your business too it is a write-off. You will allocate the % of the costs to your business expense and the other % will not be a write--off because it is a personal expense. So if your membership costs $100 and you use 50% for business purchases and 50% for personal then your business expense and write-off will be $50. This will require you to do an analysis each month based on the total amount spent to determine the write-off portion (supporting documentation).
The same accounting applies for if you use your personal cell phone for business use and submit an expense report... the company can write-off the portion that they reimburse you for as a business expense for phone services because it is ordinary and necessary for an employee to use their personal cell phone to conduct business sometimes.
