Straight marines would be tricker but based on what you're saying I think the Vanguard and Sternguard Veterans datasheets might cover the Veteran Squads you mentioned, again barring any more exotic weapons (eg Volkite crops up in 40k but more rarely, you may not be able to take it on codex squads even if it's fine on a Forge World vehicle from Imperial Armour).
Other than that you could probably double purpose a lot of figures by organising them into different squads in the two games (eg maybe break up a big heavy weapons squad into a Devastator squad and the heavy weapon marines of a few different tactical squads).
That kind of reuse might not be optimal but it should *work*. Particularly if Drop Pods are OK in Heresy too.
(This is all more for my own musing and anyone else thinking about double duty models; I assume Prim will be happy with strict HH for the foreseeable and we can try to tempt him into 10th edition later
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