Some functions may enable this (in particular, those that use inputParser to parse string-value pairs will always accept a struct), but clearly not all functions, as you found out when you ran your example. However, you can always pre-convert a struct to a cell of string value pairs using the utility below.
function C=struct2pairs(S)
%Turns a scalar struct S into a cell of string-value pairs C
%
% C=struct2pairs(S)
%
%If S is a cell already, it will be returned unchanged.
if iscell(S)
C=S; return
elseif length(S)>1
error 'Input must be a scalar struct or cell';
end
C=[fieldnames(S).'; struct2cell(S).'];
C=C(:).';
