I have always used my Fidelity American Express (2% cashback everywhere) to load to Serve for myself and family members and I am relieved to report that loads are working as normal.
Serve allows for $1,000 a month of free credit card loads ($1,500 if you link Serve to Softcard) so if you use your Fidelity AMEX you will get a free $20-30 per month with no fees.