If it is a slim margin, then I'm not worried about Latios' vote. But a lot of people say that Latias looks OU (I've seen very little talk otherwise). It's a wideswept margin that I'm worried about.I don't see how they could possibly be "the same Suspect twice" if Latios will almost assuredly perform most offensive sets better than Latias does right now, nor do I see some sort of pro-OU bias somehow showing up in a vote due to their similarities. If Latias just barely became OU at the end of the test after being used as an offensive threat almost exclusively, then why exactly should we be worried about being biased towards OU, when testing something that's pretty much just "a better version of the same pokemon"?
Either way, you may not have considered that successfully voting Latias into the OU tier means that it will also be present during our Latios test, and we'll effectively end up testing both of them at the same time. The circumstances will be significantly different.
The bias I mentioned wasn't meant to be a preset vote towards Latias' vote, but a "been here done that" kind of ordeal. Latios will perform the sets better; I have no doubt about that (in fact, it's what I'm afraid of). It's the general perception of a special dragon powerhouse in the metagame will be deja vu rather than a real suspect test. It won't impact the metagame much more than Latias if any (having already have dealt with a near identical threat, people will know what's coming). This advanced preparation may sway voters away from seeing a true suspect rather than seeing an everyday pokemon.
The way things are going, they're looking to be "the same suspect." Latios is more powerful, true, but he's not doing much that Latias isn't now. This may very well just be my opinion/prediction, but I don't generally jump the gun on these things.
While you do have a point about both of them possibly being present during the second test, chances are that Latias is vacant on the suspect ladder (the very reason why the test was split in the first place).