Solved
Does Boundary Blend in Creo 4 have the option for G3 curvature continuity?
...or is that limited to the upgraded Style feature?
...or is that limited to the upgraded Style feature?
No, G3 continuity does not appear to be available in surfacing features outside ISDX (Style Feature).
below shows the options available for surface tangency and curve tangency without ISDX.
Boundary Blend Surface Tangency Options.

Point to Point Curve Tangency Options:

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