As far as I know the Federal Election Committee (FEC) only prohibits contributions coming from foreign nationals and corporations but they are not strict with what kind of contributions you give to the candidate may it be an item or service as long as the value of what you are giving is within the limits the FEC has given to a particular candidate or party. The only thing I can think of when not allowing cryptocurrencies as donation is when the FEC thinks it is a threat on their current kinds of "prohibited donations", as long as the money is traceable with reference this shouldn't be an issue for their part.
It seems like the FEC is treating Bitcoin contributions like any other contribution -- not restricted like anonymous/cash contributions. That's surprising to me as I doubt the FEC is doing blockchain analysis to rule out prohibited fund sources like foreign nationals. In an audit scenario, checks and credit cards leave a much easier paper trail to analyze, especially since banks cooperate with federal regulators. That's why cash contributions are restricted like this:
Quote
Cash Contributions
Contributions of cash (currency) which in the aggregate exceed $100 from one person are
prohibited. If a committee receives a cash contribution exceeding $100, it must promptly return
the excess amount to the contributor. If an anonymous cash contribution over $50 is received,
the amount in excess of $50 must be used for some purpose unrelated to federal elections.
11 CFR 110.4(c).
Contributions of cash (currency) which in the aggregate exceed $100 from one person are
prohibited. If a committee receives a cash contribution exceeding $100, it must promptly return
the excess amount to the contributor. If an anonymous cash contribution over $50 is received,
the amount in excess of $50 must be used for some purpose unrelated to federal elections.
11 CFR 110.4(c).
