No, on the whole they won't be pulling down the same Ops as SEALs other then to relieve SEALs from tasks at this point they shouldn't be doing - MARSOC will also be tasked (with 100% certainly) the role of being a QRF for SOF DA Ops when operating together -
As for the GB comparison, again, no. MARSOC will not be running with 12-man ODA's like is the common role for many GB Teams - They will help train foreign ally fighters (so in this sense yes).
The Corps is already in the door and from what I understand, Army & Navy officers on SOCOM are not handling it well and vainly trying to figure out a way to keep the Corps from stealing the show.
Too bad, cuz its too late.
This sounds like some Corps men that need to keep it in their pants. "hold me back" types. Too old to either worry or discuss that.
As for SECDEF Rumsfeld, he has been POTUS/CIC GWB best asset since being in office and truly a leader in making our SOF community more effective and lethal. (and for the record he is a big fan of the SEALs because they have the shortest OODA loop going anywhere within the SOF community).