New hires go to whatever seat is available based on class senority. While a DC-10 back seat is possible it is not likely unless age 60 gets changed. Odds are a new hire will probably be in the back of 727, a healthy percentage will go to the 727 right seat. Occasional openings in exotic locals (Subic, Anchorage). When a bid is out you can change to whatever seat you can hold (including new hires).

Lag

Right now, the only training being done on the DC10 backseat is Age 60 guys forced out of window seats. As the DC10 fleet shrinks, the chances of getting a SO position is slim, as most of the positions are already taken by over 60 guys. As mentioned, a good portion of all the latest new-hire classes are going to the 727 FO seat.

Thanks guys. :)

How is the seat determined for newhires? As in, why are some first officers and some second officers starting off? More experience?

Also, does flight engineer time count toward your TT?

CRJ-200,
At UPS it is almost serendipity, HR hires the people and the Training Center Fleet Managers choose the most qualified to the needs of the fleet requirements at that time. Really just filling the holes left by system bids, etc.
Example: 10 new hires, open seats that class turn out to be 5 A-300 F/O's and 5 757 Intl. F/O's. The 757 Fleet Manager will likely get any with Intl experience. He can have a cut. The rest are either assigned or allowed to choose the remaining seats. Another new hire class might be split between F/O and S/O. If all domestic, they may just assign based on recency of experience in the flying seat.
Not sure FE time is all that useful at UPS. You need to meet their pilot mins. Will ask about the TT question though on Monday.

At FedEx, your seniority at initial hire is based upon your last four digits of your SSN, the higher the number, the better seniority. When you show up for class, they already know what seats and how many are needed for your specific class. Bidding goes in seniority number. There may only be s/o 727 for a particular class or all f/o 727 or a combo, each class is different.

So if you have a class date and can get your SSN changed so the last four are 9999 you're in good shape. ;)