Earlier quoted context omitted.
No and that's the problem. Gmail sees your IPs instead of the originating IPs, with a negative impact on spam classification quality, and in all likelihood a negative impact on your IP reputation due to the appearance of relaying spam.
Curious if you've encountered this problem or if its hypothetical (not to take away from your comment, it makes sense). I've had Zoho->Gmail setup for a while and I've had no issues with false positives/negatives.
I guess I've never personally tried it, but I've had to field customer problems for people who did this and who had real problems (mostly spam false positives).