I am making an RIS with an og of 1.106. Needless to say I need a lot of healthy yeast. I am pitching on to the yeast cake of a brown ale, sothe number of yeast is not a problem but i wasn’t able to buy the O2 hookup with oxygen stone as planned. If i just resort to a lot of shaking and agitation how much of an issue will it be?
You can still be ok. In this situation, I’d re-aerate after less than a day. What I would suggest is that after about 16 hours, shake/swirl the carboy again to release the CO2 that’s in suspension (be careful, so you don’t create a beer-volcano) and then shake it full of oxygen again, or better yet, rack it into a new fermenter, being very splashy to reaerate the beer.
Alternatively, reserve some yeast, and after a week of fermentation, make that reserved yeast into a starter, and pitch it into the fermenter when the starter is at high kraeusen so that you’re sure you have active healthy yeast going at the last 10 or 20 points.
Shaking it does allow for random dust and stuff to come in, so TRY to do it in a clean room. But it is high OG and there will be lots of yeast to combat baddies.
Anyway, my tip is that you can constantly shake it until fermentation takes off. Up until the point where the entire top of the beer is covered in krausen, you can shake it without fear of eventual oxidation of the beer.
Also, shake it after pitching the yeast. That way they’re in there to soak up the O2 they need. 
Got that tip from Palmer and it has worked flawlessly for me for the past 6 batches. (I don’t shake, I use a stainless pipe and pump in filtered air – no stone because stones are a PITA).
