If it isn't a corporation, there is no "corporate veil" with regard to taxation. With regard to liability, LLCs are a matter of state law, so you would have to refer to your state law to determine if using funds from your personal account would jeopardize your liability protection. I suspect that making the SEP contribution from a personal account would not affect liability protection of the LLC since doing so would serve to not reduce the assets in the business account that would available to cover liability claims.
