Yes, but only for spending from an output of the type OP_0 <20 bytes> or anything similar. The witness data must still be in the transaction when you are spending from an output that has anything like OP_CHECKSIG in the output script.
old clients wont check whats after 0x00(op_0).. they automatically treat the transaction as valid.
again the signatures are not in the same expected area. segwit abuses 0x00 to achieve this. thats the whole point of how segwit can work as a softfork!
because the signatures are not where they are expected. old clients treat it as just a valid funky tx.
the 20 bytes after 0x00 (op_0) are not going to be what old clients expect to see. yet they would automatically look passed it, without care.
i think you are blindly trusting the dev's to make pretty code with zero bugs. instead of thinking with a critical mind that things can break and to think that its better to have a things might break mindset rather then a devoted faith that it will elegantly work. because blind faith is the mindset of people who wont bug check/hack it to its limits. they will just do a couple standard transactions and praise their lord that funds move.. rather than trying to break it
come on.. the code is not even released and ur already thinking its perfect..
real that last line 5 times. let it settle in your head. and think about the mindset you have.
even scientists who spend years developing space rockets, still end up with them blowing up.