I brew in the keg with natural carbonation (so no CO2 for blanketing). I tried dry hopping a couple of times and it seemed to cause oxidation from the trapped air in the pellets. I'm wondering about trying a hop tea instead. I plan on steeping some Galaxy in water at about 70C. Any body tried this or have any tips?
Hop tea is a good way to get some flavour and aroma into you beer. I used a coffee plunger, which worked well. Works better for late addition flavours (but doesn't replicate dry hopping so well).
I'd be surprised if the dry hopping added a huge amount of oxidation to your beer though (the air in the pellets is so negligible that it probably didn't contribute much if anything). What flavours did you get in your beer (as it might not have ben oxidation at all).
Opening your fermenting vessel unnecessarily and agitation/stirring once fermenting are far more likely candidates than adding hops (even if fermenting in a keg).
Thousands of home brewers (and commercial brewers) have opened their fermenters added dry hops without any issue (something I've also done dozens of times).
Also, don't be fooled by the alleged "CO2 blanket". It doesn't really exist. Yes, fermenting beer will push out air from the fermenter (particularly during active fermentation) and provide some protection, but O2 is almost impossible to completely exclude. I brewed dozens of batches with natural carbonation and never had an issue with oxidation (even with heavily dry hopped beers), so I'd be interested to know what you're doing so we can possibly provide some insight.