The idea of community elected seats is just that; the electors are members of the community. So if we decide that employees of community organizations, like the WMF, are part of the Wikimedia community... then they should have the right to vote on community seats of the Board of Trustees. Whether any individual member of the community has a second opportunity to influence the composition of the board is irrelevant to determining whether they should have suffrage as a member of the global community.
Not to put too fine a point on it, but there are many people eligible to vote in the election that also have chapter affiliations which give them a voice in the chapter-appointed seats. Since we don't disenfranchise them for their "double vote" power, we should not disenfranchise other people that meet our working definition of who counts as a member of the community. Either staff employed on behalf of the movement count everywhere, or they don't count at all; there is no reason I can see that employees of the WMF are more entitled to vote than, say, employees of WMDE.