my snowflake doesn't touch my urchins (4 tuxedo's of them differant sizes) but when i had a really bad infestation of bryopsis i was told to raise the ph level to 8.6 area - it slowed it down but didn't get rid of it - ended up taking out alot of the rock and doing a quick pressure wash on them to clean them off. Was worried it would send my no2 and no3 out the roof but they didn't change from 0. (guess its like a quick fresh water dip) Finally got rid of the bryopsis by having a fire in the house - drawback was it also got rid of everything else
If you only have it on a couple rocks why risk a full on spreading - take them out - just my personal preferance after not winning the last battle. I am sure some one has won the battle and can share.