Well to start with, Raam’s reversal is strike invincible, not throw invincible. So he’s got to guess just like everyone else without a DP on his wakeup. In my experience he is in fact quite free to Hisako once he’s been knocked down.
On the other note, I’ll test when I get home, but I’m reasonably sure that he doesn’t get a strict punish on heavy rekka with (normal) command grab. Hisako can punish jump-outs with heavy rekka for a full grounded combo, which means she’s hitting them while they’re still in their 4 frames of pre-jump animation. Raam’s grab hits on frame 4, so at most I think it would try to trade with HP rekka, a trade I would imagine the rekka would win. If Sako delays the heavy rekka slightly then I guess Raam wins, but this isn’t materially all that different from doing rekka against anyone with an invincible DP. Mash DP will always beat any of Hisako’s rekka options, but it isn’t actually all that common to see, just because mashing moves in between rekka strings can be tricky. QCF/QCB is definitely easier to squeeze in there, but again, if you’re just a touch late you’re going to be eating full combo damage.
Hisako’s command grabs are also generally more active than Raam’s, so she tends to beat him out in any command throw-vs-command throw encounter. He can certainly grab at further ranges than her, but if she’s in range for her own grab, you should generally expect her to win.
And on the subject of neutral, Hisako handles Raam’s “wall” a lot better than many in the cast. Her normals are long enough to contend with or outright beat his, and she’s more than fast enough to dash in from footsies range to establish her preferred spacings on him. Either of her command grabs will beat Raam’s running bear grab clean, so even if Raam can charge through her normals, if he messes up the read on one of those he walking into a fully punishable situation.
Don’t get me wrong - from what I can tell Raam absolutely mauls Hisako on her wakeup. The thing is, she pretty effectively returns the favor on his. This is pretty much the S2 Aganos/Hisako 5-5 to my mind, where the fight generally comes down to which character gets the momentum first. Either character can blow up the other once they establish their game - the only question is which character gets to establish that game first.