Is voting via email permissible in a 501c corp. in Nebraska

If it is a corporation formed under the laws of Nebraska, as in most states, it would depend on whether such voting is allowed by the articles of incorporation or by-laws. And it depends upon which type of corporation it is. See this: Nebraska Legislature - Revised Statutes Chapter 21 (http://www.legislature.ne.gov/laws/browse-chapters.php?chapter=21)

For example, this statute provides for waivers of meetings for business corporations:

"21-2054. Action without meeting.

(1) Action required or permitted by the Business Corporation Act to be taken at a shareholders' meeting may be taken without a meeting if the action is taken by all the shareholders entitled to vote on the action. The action shall be evidenced by one or more written consents describing the action taken, signed by all the shareholders entitled to vote on the action, and delivered to the corporation for inclusion in the minutes or filing with the corporate records.

(2) If not otherwise determined under section 21-2053 or 21-2057, the record date for determining shareholders entitled to take action without a meeting shall be the date the first shareholder signs the consent under subsection (1) of this section.

(3) A consent signed under this section shall have the effect of a meeting vote and may be described as such in any document.

(4) If the act requires that notice of proposed action be given to nonvoting shareholders and the action is to be taken by unanimous consent of the voting shareholders, the corporation shall give its nonvoting shareholders written notice of the proposed action at least ten days before the action is taken. The notice shall contain or be accompanied by the same material that, under the act, would have been required to be sent to nonvoting shareholders in a notice of meeting at which the proposed action would have been submitted to the shareholders for action.
" Nebraska Legislature (http://www.legislature.ne.gov/laws/statutes.php?statute=21-2054)
A similar statute may be in place for your non-profit corporation. Check and see acccording to what type it is.