Recent work show that some pathogenic Gram(-) bacteria have no functional T3SS or significantly reduced number of T3SS effectors, but have full T4SS.  There is still no other reports about dual role of bacterial effectors for both T3SS and T4SS...

Aurélie Angot with colleagues found that a number of  type III and type IV effectors  have the capacity to interfere directly with ubiquitin signaling. The bacteria use  type III and type IV effectors for the same targets to:

(i) control the timing of action of their virulence effectors,

(ii) target specific signaling intermediates involved in mammal or plant innate immunity, or

(iii) mimic specific host-like UPS components, illustrated by the bacterial FBPs.

I can give indirect support for the idea that some effector classes can be transported via  both type III and type IV SS.

Angot, A., Vergunst, A., Genin, S. and Peeters, N., 2007. Exploitation of eukaryotic ubiquitin signaling pathways by effectors translocated by bacterial type III and type IV secretion systems. PLoS Pathog, 3(1), p.e3.

Is where any new conformation for the conclusion made by A. Hubber?

Hubber A, Vergunst AC, Sullivan JT, Hooykaas PJ, Ronson CW. Symbiotic phenotypes and translocated effector proteins of the Mesorhizobium loti strain R7A VirB/D4 type IV secretion system. Molecular microbiology. 2004 Oct;54(2):561-74. :

"Nevertheless, the comparisons between R7A and MAFF303099, including the identical mutant phenotypes of the respective T4SS and T3SS mutants on L. leucocephala, strongly suggest that the type IV and type III systems are interchangeable. Over the course of evolution, bacteria can adopt either, perhaps with functionally redundant effector proteins, to translocate proteins to eukaryotic hosts."