But he hopes they will not create pressure to increase salaries in Wales.
There is an agreement which limits the regions bidding for each other's players, however Scarlets faced competition when re-signing centre Scott Williams who was out of contract at the end of the season.
"You've got to be realistic because it is a free market," Short said.
"No agreement can constrain someone's ability to look for work, and regions will be ambitious and will have their own player requirements.
"How the financial fallout from that works is part of the regions' agreement, and one would hope that you wouldn't see pressure within Wales to increase salaries because we've got enough to deal with outside of Wales."
Wales international Williams had been expected to renew his national dual contract (NDC), funded 60% by the Welsh Rugby Union (WRU).
However, the WRU withdrew their offer with union chairman Gareth Davies saying it was because the regions had "upped the ante".
Williams ended up signing a conventional deal with the Scarlets.
The NDCs were introduced as a mechanism to stop high-profile players leaving Wales for England and France.
Short was chairman of the regions' representative body - now called Pro Rugby Wales - when they negotiated the deal which funds and governs domestic rugby in Wales.
He said he would not have expected the union to get involved in a bidding war, and backed the dual contracts.
"The union have been excellent in supporting regions in the past year," he added.
"The NDCs are working well and everybody should recognise that it's a new concept and will take some time to settle down, but it is settling down well.
"And congratulations to the union - it's been a sea-change in the relationship over the past year or so."

He has been recalled by Cricket Australia for treatment on a foot injury suffered while bowling during the County Championship loss to Sussex.
The county hope New Zealand's Mitchell Santner, who is playing in the T20 Blast, can be his overseas replacement.
Hastings, 31, has taken 16 wickets at 34.38 and scored 139 runs at 23.16 in his six Championship games this summer.
On Friday, he hit the second fastest Twenty20 half-century in Worcestershire's history off 19 balls against Birmingham Bears.
Director of cricket Steve Rhodes told BBC Hereford & Worcester: "Cricket Australia have asked for him to go back home.
"We thoroughly understand that - they want John Hastings back fit and want to monitor his rehab, so we'll take it on the chin.
"We'll certainly look at alternatives. In the past we've brought in Miguel Cummins, Kemar Roach and Shannon Gabriel but the West Indies are here this year.
"So we've just got the find the right one because we're desperate to go up."
Worcestershire are currently second in Division Two of the County Championship, 17 points clear of both Sussex and Kent, who have a game in hand.
Scarlets chairman Nigel Short admits it will be hard to stop regions competing against each other for Welsh players.
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Worcestershire will be without Australia all-rounder John Hastings for the remainder of the 2017 season.